How-To: Make Your Own Road Construction Sign
OK, so it may not strictly be a tool — although it is done using a computer, which is a tool we use for reading TM — but it is a lot of fun. The site offers other options including building, gas station, and highway signs. You can also do computer error messages:

Atom Smasher [Manufacturer’s Site]
And for those who want to try the real thing.
http://toolmonger.com/2009/09/29/how-to-make-your-own-road-construction-sign/#comment-1033666
wrong link, here’s the right one.
http://www.i-hacked.com/content/view/274/48/