First comment, it can be understood as "tag" in the graffiti sense but also in the geotag meaning (i.e. linking content such as text/music/pictures to geographical data). Although it's not a common practice in cities, it's intriguing to see such warning from a possible near future. I'm not sure geotagging will spread but I find pertinent to see how creating such warning include that technology-mediated practice in a sort of "design fiction" narrative: it actually reveals the possibilities and let people (who understands it), wonder about what can be the proper usage.

Second comment, as Timo would say: "it's also serif font on a black background".