[Edit - This post was originally from Jan 19th, 2010. I've updated it with information about the "Mystery Missile" contrail of Nov 8, 2010, at the bottom of this post. Clearly it's the same thing]
[Edit again - I've mirrored this here as apparently my contrailscience.com server is crashing, sorry]
An interesting contrail cropped up off the coast of San Clemente, Orange County, California on December 31st 2009. The curious shape led some people to think it’s a missile launch, which it does kind of look like (all taken from San Clemente)
Here's another possible mystery missile explanation. But IMO, the jury's still out, otherwise the DoD would have conveniently used the jet contrail explanation, although they still might. To read the rest of article, click here.