Get a pack of the clear plastic screen protectors made for PDAs. Get the kind that has no adhesive. Trim it to size, clean & dry the reflective surface of your signal mirror, then apply it. Leave enough of a tab to pull it away with. I wrote "PEEL OFF" in red marker on mine 'cuz the stuff is very clear yet would still impede reflection to some degree.

Works great and keeps your mirror scratch-free as it rides in your PSK.