This is not exactly an exciting sign, but it's a little different method so I thought I'd share.
One of the more upscale parking garages prefers this type of sign for a classier look than just vinyl lettering on the surface. The added advantage is no one can pick at the letters.
It's clear 1/8" acrylic. The vinyl lettering/arrow are cut in reverse and applied to the back. Then I spray it with the background color. After the paint is dry, I sheet the back with scraps of vinyl to protect the paint in the mounting process.