If you hike by yourself and don't pack a signaling mirror, I would suggest carrying one in your first aid pack. I fell near the top of a 14,000 foot peak some time ago and cut my chin. The mirror allowed me to see what I was doing as I cleaned the wound and applied several butterfly bandages. It eventually took 7 sutures to treat the injury and the emergency room physician complimented me on how well I had applied the bandages.

I also find a mirror handy for removing debris from the eye when no one else is available to assist.