Piggy Backing Ads

Lately I've been noticing a trend of one company piggy backing off another company's already established advertisement. BMW and a paint recycling company, RONA, have billboards that either counter a competitor's or plays off an already well establish company. We're getting so green now that we're even reusing ads.



BMW played off of Audi's billboard who taunted BMW saying, "Your move BMW". Apparantly BMW took it seriously and made a big move with its much bigger ad with a sly reply.




RONA did something similar without the aggressiveness. They took an already well established ad, iPod Nanos, and used it as an extension of their own ad. I wonder if there are rules for that, if not I could see lots of interesting possibilities.