You could vacuum seal it (you DO have one of those neato things don't you), then cut a tear notch in the side of the plastic bag so that you could open it easily...

How about one of those plastic inserts for your wallet? It holds 5 or 6 credit cards and has a plastic flap that you slot into your wallet to hold it in place. Cut off one of the pouches (signal mirrors are credit-card sized, IIRC) then put the mirror in that and tape over it. Works for fresnel lenses too as they are also credit-card sized.

A

I tried the bike inner-tube route myself on my mirrors. I took one out a while back to find it so scrached that it was unusable. Evidently some dust or dirt got under the band and 'polished' it to a matt finish. I use the plastic mirrors for weight savings, glass ones might be tougher. I'm going to try lining the mirrored part with something like electrical tape to see if that will help protect them a little better. Also, someone in here suggested clear plastic adhesive-backed film used for protecting PDA screens, that might be the route to go. - Dave