Don't try the sign activity shown on the site urlesque: exposing bit of the web--it's against the law! Just look here to discover some really creative ways people have altered STOP signs.
The stop sign got me thinking about the universal signs and symbols that we have come to take for granted. That thought led me to an article, "Navigating Today’s Signs: An Interview with Mies Hora," from the professional design organization AIGA. Mies Hora is a "sign and symbol maven." It's an interesting article about sign literacy. I'd never even considered literacy in relation to signs, that's because I've always taken it for granted. Check out the images on the right-hand side of the page where you'll find the stop sign (fig. 2).
Signs have been around nearly forever, or at least as far back as the people who made cave drawings. In more recent history, signs have been used to advertise. We have a fantastic photo-illustrated book called Designage: The Art of the Decorative Sign by Arnold Schwartzman [741.6 SCH]. Sit down and peruse it the next time you visit--you don't need to be sign literate to enjoy it!