I saw this same article. The idea makes absolutely no sense. For one thing, it's pretty much illegal, and the homeowner could face a daily penalty under most city codes of $200 to $1,000 per day. You cannot place advertisements like this in residential areas under most ordinances -- and you would think that the guy doing this would have already researched that.
The bigger problem, other than the legal problem, is that the traffic count on residential streets is incredibly low -- maybe a few hundred cars a day in some areas. Who wants to pay money to reach a market that small? Sure, on this first house they made the national news and that's a big audience. But the signs themselves reached practically nobody.
I'm not even sure that the whole intent of this P.R. stunt was not just to get free national news for Brainiac, and the homeowner was just the pawn in that P.R. stunt. But if they got paid, then I guess that's O.K.