Too many things can damage the mirrors.
Jan- with all due respect -
NONSENSE-
Very little will damage the front side of a mirror besides abrasion (scratching) and even that is difficult to do. All a mirror is - is a piece of glass with a reflective surface on the back. The back is the sensitive side and I agree that various adhesives can cause trouble if you attach them to the BACK.
I just taught a class in Anaheim at the PPFA Convention called;
Installing Art on Difficult Surfaces. One of the surfaces we discussed was mirror, glass and smooth stone (i.e. Granite like fireplaces).
A major part of my income comes from installation services. There is a great way to do it. It won't harm the mirrors. It is completely reversible. I have hung very heavy pieces this way.
Command Adhesive is very effective and I have used it with great success in the past, especially for lighter pieces. I use the adhesive, but not the hooks.
However, Paul does have the right idea, in that one does not know how the mirrors were installed in the first place, and the OP doesn't provide enough information to make an accurate suggestion. Are they held with mastic to the wall and a j moulding at the bottom? Was the wall primed first? Mirror clips alone? Do they run floor to ceiling?
Mirrors that run to the floor will rarely be affected by shear weight on a hook from something being attached to them.
I won't post how to do it on the Grumble because I agree with what Jared posted re: feeling that you don't have to go to the shows because someone will always post what you missed.