Happily, I can report the BAA's information staff are trained in body language.
A Sardinian woman asks if it is easy to find a taxi at Heathrow. The answer she gets is a cheery British thumbs up. (Very likely from one of the 900 cabbies who serve the airport on an average day.) Immediately, she clonks the unfortunate man whit her handbag for making such a devastatingly insulting suggestion. This is why, incidentally, it's not a very good idea to thumb a lift in Sardinia.