Citations:bull's-eye

Noun

 * 1) * 1875, George Hayter Chubb, Protection from fire and thieves including the construction of locks, safes, strong-rooms, and fireproof buildings : burglary, and the means of preventing it; fire, its detection, prevention, and extinction; etc. : also a complete list of patents for locks and safes,, page 36:
 * this padlock being visible, the police in their rounds can tell by a glance under the light of the bull's-eye whether or not it has been interfered with.