Lights and stuff on regular cars, replica police cars, that's pretty interesting.
Quick search - there are cop car collectors, here's some of the basics of "cop car collecting:"
http://www.allpar.com/squads/collecting.html
An excerpt regarding flashing lights, etc.:
"We are constantly guarding against irresponsible behavior by other police car hobbyists. The impersonators have helped to make our lives a bit harder also. Some legislators do not see the difference between hobbyists and impersonators. Many of us are working very hard to try to change this and there has been some success and the work is ongoing. There also have been some failures such as in New Hampshire where the mounting of any lights on any vehicles now (as of 2007) requires a permit which is almost impossible for hobbyists to get. In Colorado, the ownership of red and blue lights by private individuals is illegal. We can only hope that this doesn’t continue to spread to other states, or worse…become Federal legislation. It is up to each and every one of us to see that this does not happen. Responsible ownership and operation of our vehicles is paramount."