The proven mechanism of graffiti is that one tag, no matter how innocuous, inevitably attracts many others that may be totally unrelated to that first one. I've lived through this, I know the pattern. The sight of one prominent tag being allowed to remain is taken as a sign to others that (a) residents of the neighborhood don't care ("they're cool") and (b) there aren't likely to be any unpleasant downsides like getting caught or confronted. Everything has to start somewhere and a graffiti plague begins with The First Tag. The green light is signaled. Unfortunately, they don't wake you up in the middle of the night and offer you the option to accept only the "harmless" tags about bike safety while meanwhile rejecting the idiots and gang-banger tags. You end up having to live with ALL of it. The waste company that owns those dumpsters should be pestered with phone calls that the dumpsters must be painted over immediately, too. In some communities, there's a legal responsibility for businesses to paint over tags ASAP.
