Whoa guys, isn't there a slightly more subtle way of getting the message across? How about "your phone could possibly, perhaps, maybe cause the fumes to ignite and you may, might, could get terribly injured"? :)
Aside from the text and its bluntness, the thing that I found amusing about the photo was the "Serious about service" tagline at the bottom of the sign. Not that I'm suggesting that Total's not serious about service - they're as good as the next filling station; but the contrast in tone is pretty funny, don't you think?