Rescue Flash Mirror

Visible over 20 miles, durable LEXAN® polycarbonate mirror with mil-spec retro-reflective aiming aid for one-handed use.  WEIGHT: 0.32 oz  SIZE: 3” tall x 2” wide.

From Backpacker Magazine Oct 2006:

Despite its small size, this mirror produced an obvious reflection. A tiny retroreflective mesh aiming window in the center of its scratch-prone Lexan surface lets you point the signal with surprising accuracy. Testers dubbed it "most likely to get packed" because of its minimal weight and size.