If you think putting URLs on shirts is bad, I have a Nuclear Assault t-shirt somewhere that has their old mailing address printed on the back.
Route 666 seems appropriate, but it's been on Maiden shirts, AC/DC websites, comic books, and it's just a little hackneyed by this point.
that said, and a little off-topic, I found this interestingly little history about the
real U.S. Route 666 (which ran through desolate areas of New Mexico, Colorado, and Utah) on the US Dept of Transportation's website:
http://www.fhwa.dot.gov/infrastructure/us666.htm
Named as such because it was the sixth major highway to branch off of the famous Route 66.
Sadly, two summers ago it was renumbered with the much less demonic "US Route 491"... Again, I blame Bush.