Make your own gas station sign
Here's a site that lets you engage in some low-intensity culture jamming by making your own Exxon sign. Just type in the text of what you want the sign to say, and the good people at Atom Smasher will do the rest.
Best of all, the site gives you permission to copy the image and post it on your own site, without fear of legal retribution from Atom Smasher. I can't say the same for Exxon....