Another thought I had was to create QR codes, and have them made into a sticker or card that could be applied to the trailer, taped to the window, or whatever. For anyone not familiar with QR codes, these are the little black and white squares you can scan with your mobile phone to take you directly to a web site. To create the codes it is quite simple:
1) Go to http://goo.gl, Google's URL shortening service.
2) Paste in the URL to your build thread or album and click "Shorten URL"
3) Copy the shortened URL. In my case, it is http://goo.gl/yrPzYx
4) Paste the shortened URL back into the URL of your browser, add a ".qr" onto the end, like this: http://goo.gl/yrPzYx.qr, and then hit Enter.
5) This will display the QR code, which you can print. You can actually test the code on screen directly from your mobile phone using the Google search app (Google Goggles) or any other QR code scanner.