Two things I've seen recently that I keep meaning to get a photo of but failing.
1. Tom Tom Billboard Advert
"You are not in traffic. You are traffic" Great message, especially when allied to the 'Break Free' tagline. Except the 'Break Free' doesn't mean getting out of your car (this is an ad for an in-car satnav of course) but rather get a Tom Tom so you can find the routes without traffic so you can take that instead, thereby, presumably, creating traffic.
2. Sticker on Royal Mail vans
"This vehicle is limited to 70mph for environmental reasons" What about legal reasons what with being the fastest any vehicle is techically allowed to go on the roads in the UK? Even more meaningless on those citylimited vans...