This study aimed to investigate the language usage of outdoor advertisements and find ways to improve it from the perspective of public language. Anyone is exposed to signboards without limitations, and it allows the public to learn fixed language forms for a long time. Therefore, it has both direct and indirect effects on the public’s language lives. This study focuses on sign language as a public language. Here, signboards from four districts in Gyeonggi-do were collected and analyzed in three ways. Signboards marked only in Korean accounted for a relatively large proportion of the main words, whereas mixed types of characters were used together in the subwords. In addition, there were cases of intentional violation of the language norm and listed only the initial consonants, those conscious of ambiguity. Results show that follow-up studies, such as conducting an additional survey, designating a demonstration area for the practical maintenance of sign language, and preparing guidelines for the production of outdoor advertisements, are expected to continue.