This one is for all the transport nerds and the War chalking/war driving geeks. Article courtesy of Gizmodo.com:
Here's a neat Instructable for significantly increasing the geek factor in your car's rear windshield, showing how to modify a Wi-Fi-detecting t-shirt into a Wi-Fi-detecting bumper sticker. At some point in some traffic jam, you'll make a fellow nerd's day.
Starting with a novelty t-shirt that displays the strength of Wi-Fi signals in the area, an Instructable user lived up to his matching user name and license plate of "MacGeek" by hacking together this Wi-Fi detecting bumper sticker.
Click here to read the entire article and for some more pictures. Of course, here is the "How To" info if you got some time and interest in helping that next car guy/girl who is starving for 802.11 love.
If you are doing it, let me know if it worked for you.