spotter

One that applies spots.

One that looks for, locates, and reports something, as.

A military or civil defense lookout.

A person hired to detect dishonest acts by employees, as in a bank.

One who identifies players on the field, as for a radio or television announcer.

One who is responsible for watching and guarding a performer during practice to prevent injury, as in gymnastics or weightlifting.

One employed by a dry cleaner to remove spots.

One who or that which spots; specifically, one who is employed to shadow suspicious or suspected persons; a detective.

Specifically, a person employed to keep secret watch on the employees of a company, especially on a street railway to spot or note the number of fares (if any) not turned in by the conductor.