My response:

The bumper stickers I made myself worked very poorly. I tried spraying them
with fixative and covering them with clear packing tape, but they weathered
badly anyway, and the color ink faded in the sunlight. (The black ink faded
much more slowly.) I never got around to trying laminating, because I
couldn't think of a good way to secure them. (I had printed earlier ones on
label paper.) Epoxy would do it, but then I'd never be able to remove them.
The packing tape also weathered badly, eventually becoming brittle, and
refusing to come off in a couple of spots.

I eventually went to the custom printing store at Crossgates Mall (Mugs N'
More). I gave them the text for three of my four bumper stickers, and the
URL for the graphical one I had designed ("Jingoism"). They did the
printing with all weatherproof materials, and I've been pretty happy with
the results. But the color one is fading in the sunlight again. (Luckily,
I had outlined the letters in black to help the contrast, so the word is
still legible even though the image as a whole is nearly gone.)