In recent decades, many cities have started to change towards a greener, more sustainable and more resilient model of urban development. They are investing in forests, wetlands and other green spaces—“green infrastructure” [
1]. Urban forests can be broadly defined as the natural and planted trees in urban areas [
2]. Forest resources can significantly improve the quality of the urban environment and the wellbeing of its inhabitants [
3]. Properly planned and managed urban and per urban forests provide important positive externalities through ecosystem services. These services and values include, as McPherson et al. [
4], Bolund and Hunhammar [
5] and Ordóñez and Duinker [
2] claim: clean air and water, energy conservation, carbon storage and sequestration, cooler and more regulated air temperatures, wildlife habitat, recreational opportunities, social, physical and psychological wellbeing, aesthetic quality, emotional and spiritual benefits and economic values (increased real-estate values, savings due to carbon dioxide sequestration and air pollutant removal, among others). Sustainable urban forests may be broadly defined as the persistence or continuation of a system over time. A review of useful definitions of this term can be found in the publication of Ordóñez and Duinker [
2]. Sustainable urban forests cannot be separated from the activities of humans. Such activity can be both positive and negative. Wide-ranging activities of people are among the major forces for change in the health and character of the urban forest and ultimately determine its sustainability, more so than with any other forest resource [
3,
6]. The adverse impacts of humans can be mitigated by positive actions such as planning, planting and management; all occurring with common commitment and shared vision. Managers of urban green spaces (both public and private), as Clark, Matheny, Cross and Wake [
7] note, must involve the surrounding community in decisions and actions regarding urban forests. The use of urban forests provides opportunities for citizens to appreciate and learn about natural resources. According to Sondergaard [
8], nature interpretation is considered to be an essential part of both recreation and tourism. The importance of urban forests and green spaces is increasing, because the number of people living in towns is growing. The experiences that urban residents have with trees and associated resources in the urban environment are likely to influence their perceptions, expectations and use of more distant natural resource areas, such as national forests, parks and monuments [
3]. The results of Eaton’s [
9] study demonstrate that outdoor education programs are effective for promoting cognitive changes in students. Lindemann-Matthies’ [
10,
11] research on promoting opportunities for children to experience nature directly on their way to school suggests that teachers should make greater use of educational approaches that focus on direct experiences in children’s local environments. Ecological education conducted in forests is aimed at passing on the knowledge about the natural environment and the functions of forests, as well as shaping a pro-ecological system of values and triggering activities for the protection of the natural world. Environmental education programs can enhance the recreational services of urban forests for visitors [
12]. According to Ja-Choon et al. [
12] environmental education programs in urban forests can be categorized into two types by the presence of signs or interpreters. Without interpreters, a self-guided environmental education program can be provided through signs located along the trail. The occurrence of recreational infrastructure in forests, which includes interpretive signs, has strong links to public use of the forest environment [
13]. Roads or marked trails will attract and concentrate visitors to particular areas. Such infrastructure, however, can negatively affect those seeking wilderness areas without signs of human activity [
14,
15]. According to Wielgus [
16], the relationship of an engineering facility to the landscape is not widely appreciated, meaning that many emerging facilities are disconnected from their environment, lacking a synergistic display of value along with landscape assets. Vidiella [
17] points out that with the introduction of the concept of sustainability into the design of buildings, an increase has been noticed in the number of buildings that meet or seek to meet the principles of green building, being environmentally friendly but also creating harmony with the surrounding landscape.
Ballantyne and Hughes [
18] point out that the number of visitors to nature sites has increased in recent years, which also means an increase in the demands put on workers working in nature sites. Site managers have responded to this pressure by installing in situ visitor signs to inform visitors about the features, events and/or facilities they encounter. Well-designed interpretative signs can play a key role in developing positive environmental attitudes and behaviors [
19,
20] and foster attachment to the site and identification with the area [
21]. There is a large number of publications showing how to design interpretation panels and signs in closed spaces such as museums and visitor centers [
22,
23,
24,
25]. Much smaller is the number of guides for designing interpretative signs outdoors, in national parks and forests, including urban forests [
21,
26]. According to Wolf, Stricker and Hagenloh [
27], guidelines for the design of closed spaces cannot be always used outdoors. In the open air, interpretative media have to be particularly effective in communication because of the presence of many random sensory stimuli that are not conducive to concentration [
18]. Moscardo et al. [
26] note that another issue related to signs interpreting nature is that a sign is always static, while nature, including animal behavior, is dynamic. The effectiveness of information communication depends on how it is presented, how much and how well it is arranged and how many images it contains [
19,
28,
29]. Graphic techniques make it possible to give a visual image to interpretative content in order to better illustrate the information. Whatever the subject matter, signs should be written in conversational tone with limited use of jargon and technical terms [
30] or those borrowed from the professional language of foresters, as well as abbreviations of tree species, forest habitat types without explanation and Latin names of organisms and plant communities [
31]. Professor Mike Wingfield, IUFRO ex-President, during his speech at the last IUFRO World Congress in Brazil, in Curitiba, said that the risks identified by scientists and the solutions and sustainable options for the future of the world’s forests should be used by decision makers and the broader public to reduce global crises such as climate change. He expressed the opinion that “it is crucial to present the best possible science in an accessible language and to engage with policy makers and political processes. This will allow the world’s decision makers to ‘unite behind the science and then take real action’, as Greta Thunberg has recently demanded” he added [
32]. Seretny [
33] points out that difficult texts in which new words are piled up on top of each other may significantly reduce the level of motivation of the learners. A material too difficult is often counterproductive. Instead of stimulating the learning process, acquiring new information, it extinguishes involvement, causes reluctance or a feeling of failure. Ballantyne et al. [
30] and Serrell [
34] show that interpretative signs for the general public are most accessible when they are written in a language understood by 10–12-year-olds. The level of intelligibility of the text is tested with the use of a variety of tools. The handbook “Nova Scotia. Outdoor interpretive signage. Tourism development guideline” recommends using Gunning’s (Fog Index) or Flesch’s (reading ease scale) legibility tests for this purpose. According to Łopacińska and Wnuk [
35], public studies in particular should be characterized by the use of readability indexes. In Poland, apart from pointing out general deficiencies concerning the educational message of interpretive signs, no research has been conducted in the outdoors to determine the degree of readability of educational texts. Our research was aimed at determining the groups to whom interpretive signs in urban forests are addressed, and thus assessing the level of comprehensibility of their contents. Planning the research, a hypothesis was posed that a large part of society may have a problem with interpretation of the content presented on didactic paths in the city forests of Warsaw, because it is transmitted in a language that is too difficult to understand.