I agree with the other comments that it's still very clearly vandalism, because to remove the mark, the owner would have to scrub an entire surface at great expense. Just because dirt is being removed to create the work doesn't prevent it being vandalism. With regards the commercial adverts, I'd much rather see an old, worn street than a bloody advert shaved into one of the few remaining spaces they can't normally use to hawk us products. It's not even a new idea.
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