Why are these things allowed? They contribute to traffic and pollution… and, I guess, capitalism. Did I just answer my own question?
It’s a truck with a cab and nothing else but a big sign on the back. No real cargo. No passengers. Just a huge sign… on wheels.
:mad:
But it’s COOL.
Actually, since novelty is its only advantage as an advertising medium, the more there are, the less effective they will be.
Why are they allowed? Because advertising is allowed,and if you put a sign on a building, you need to comply with local ordinances, pay a fee, blah, blah, and things that don’t change fail to attact the attention of Joe Average who…OOH SHINY! only notices new shite.
So, rather than have a fixed billboard, you put it on wheels, haul it around town, escape many of the ordinances, keep it fresh, for Joe Average and his nanosecond attention span, and mebbe employ a couple of folks at Mobile Signs R Us, too.
Or my hypothesis is full of crap. 
I agree they are lame, and people are usually paying more attention to what’s on the billboard than the traffic.
I missed this thread before but found it on a search after encountering one of these godforsaken, despicable BUZZ contraptions on the way home yesterday.
“There is a lot of advertising clutter in the world today. And with Tivo™, satellite radio, and pop-up blockers, people are avoiding traditional advertising, making it less and less effective.”
So you’ve found a new way to force the crap on people they’re emphatically trying to avoid? These suuuuuuuuck!!!
They distract the attention of drivers from where it should be, watching the road.
They increase congestion on what can be already overcrowded streets.
They waste gasoline and further pollute the atmosphere, doing nothing more than just driving around, at a time when everyone’s consciousness should be raised about prudent conservation.
Any one of these reasons should be a deal breaker, yet here the goddamn things are. I hate 'em and will not only avoid doing commerce with any business that advertises on them, but will contact said company to voice my displeasure as well. Sign of the apocalypse, indeed. Okay, maybe just the mini-apocalype… but they still suck.