Login or register (free and only takes a few minutes) to participate in this question.
You will also have access to many other tools and opportunities designed for those who have language-related jobs (or are passionate about them). Participation is free and the site has a strict confidentiality policy.
Explanation: I think they're talking about taking out ads on the backs of buses. There are lots of hits for this on Google in Spanish and in English. Plus, this way you'll avoid accidental double entendres...
Good luck!
-------------------------------------------------- Note added at 10 mins (2006-03-27 13:18:22 GMT) --------------------------------------------------
For example, here's a page that describes all sorts of ads that can be put on buses, including bus-back ads:
Actually, the list of applicable hits is pretty long.
I'd just note that if you don't like "bus backs" (in plural), you could also try "bus back advertising" (with or without the hyphen), which also turns up all sorts of ad agency pages and projects.
I went with bus back advertising in the end, tho Heather's suggestion was also excellent I thought, thanks to you all
Heather, by the way, I was joking about putting "backsides", tho doubtlessly someone will come up with the idea one day of selling buttspace so to speak :o) 4 KudoZ points were awarded for this answer
The translation workplace 
peer agreement (net): +4