Even as artistic as these things are. Even if it is art, and as much as I like it, if its posted on the walls of streets without the permission of the business owner, by definition it is "vandalism." Whether the city wants to press charges or not, they have full right too because its within their legal rights.
This is not vandalism. This is art. Should you have the passion and talent I think you should be allowed to create art like this. It is a completely different story to spray scribbles and sloppy words all over the place that make the place look trashy because you think its cool. I wish people put more effort into their graffiti & actually make it worth looking at like this, i absolutely love looking at real graffiti art. (:
Yes, it's vandalism. Yes, it's illegal. No amount of skill or creativity can change that.
But we as a society are the ones that create stigmas surrounding words like "vandal." It's all semiotics. Instead of getting all hot under the collar trying to change the definitions of these words, just keep them and work toward redefining your personal perceptions of moral and immoral behaviour.