insidious or beguiling? really clever law enforcement

let's say that you don't happen to share my affection for the fine art of concert flyers. how would you stop "rogue promoters" from papering the halls, walls, and buses of your fair city with gig posters? in glasgow, the city council cleverly started slapping CANCELLED stickers over the offending posters. the result?

... some rogue promoters ... have been inundated with complaints from music fans.
People who have bought tickets to some of this summer's big gigs have complained, thinking that an event, rather than the advert, had been cancelled.
The source said: "If people start phoning concert promoters complaining that they thought the gig had been cancelled, then the promoters have no-one but themselves to blame for having the posters put up in the first place."

i give them 10 out 10 for style, 10 out of 10 for creativity, and maybe 3 out of 9 zillion for enforcement priorities. but dang that's clever.