I did a quick search and didn't find that this had been posted.
http://bike.shimano.com/publish/cont...k_release.html
The potential for catastrophic failure makes this frightening. Check your skewers if: a) They're Shimano; b) They're silver; c) Made after Nov. 1, 2005.
The link walks you through the identification process. Applies to Road, MTB and Sport QRs.