A mirror is currently a useless item, and often considered as junk.
A mirror has no use, being added purely for the purpose of clutter, creating more realism for the player when looting.
Mirrors can be found in bathrooms and some stores.
From newitems.txt (Project Zomboid directory/media/scripts/)
Weight = 0.2,
Type = Normal,
DisplayName = Mirror,
Icon = Mirror,
MetalValue = 2,