This was an interesting trend in graffiti: lacking self-publishing resources, steal a bunch of post office labels for a canvas. Grab a stack of these from the courtesy desk, write out your tag or slogan, then go around down and slap them to any available surface. Very handy if you're too scared to stand in place long enough to write out your tag.
Wish I could remember whose quote it was: "The blank wall is the idiot's canvas."
In no sense do I support or admire vandalism. I choose to see little distinction between a street artist and a crude tagger: they are each forms of fascism, in which one person decides his values supersede those of others--in this case, those of the property owner. I can admire a street artist's work, but I will always wish he chose a legitimate venue by which to succeed, rather than expressing himself at the expense of someone else's rights.
That said, it's not impossible to admire the techniques of one's enemy. Just as we can be impressed by the persistence of the cockroach or the robustness of the latest season's flu virus, so can I admire the resourcefulness of a vandal. If you really, really don't want to spend any money, where would you go to look for free stickers? And if by radical chance you happen to know someone with a legitimate job, you could ask him to swipe a couple markers for your craft. All that's left is for you to refine your misguided and misapplied calligraphy, then disseminate your non-message throughout town for everyone to see and not understand. Awesome: way to fail to communicate anything of value. You have achieved nothing useful and only worsened your living environment.
Plus, you stole supplies from the post office. That's pretty sad, stealing something that's free from people who legitimately need it. Yeah, vandals are somewhere just above pond scum in the grand scale, somewhere below jackals and carp.