K, so after my last post I decided I'd better research this a little....

Looks like it's true, there is a Darth Vader Gargoyl (also called a grotesque) atop the National Cathedral, crazy, huh?
http://www.fraudwasteabuse.com/2007/03/darth-vader-is-watching-you-from-the-washington-national-cathedral.html
http://www.nationalcathedral.org/pdfs/darth.pdf

Menacing Darth Vader and Squirrel Gargoyles on DC's National Cathedral
Originally uploaded by expatmonkey