For our non-American friends who may not be familiar with "Selective Service," it's basically when you go to a U.S. military recruiting depot to register for the draft just in case a major war breaks out and the draft is re-instated. All American (citizen) males and permanent resident (immigrant) males have to do this within 30 days of turning 18, or within 30 days of being naturalized prior to their 46th birthday.
http://en.wikipedia.org/wiki/Selective_Service_System
This is an issue that I find feminists are oddly silent about. If men are forced to sign up for selective service when they turn 18, then why shouldn't women be, all things being equal?