I own some property in SE Arizona that used to be on Route 666 until they changed it to Route 191 because people kept stealing the signs.
http://en.wikipedia.org/wiki/U.S._Route_191
"In 1992, Arizona requested a new number for its portion of U.S. Route 666, arguing the road signs on this highway were the most frequently stolen in the state. As a result, US 191 was extended to the Mexican border at Douglas, Arizona."