Survey monument
Also called: property pin, survey pin, corner marker, property marker, iron pin, boundary marker
The physical marker a surveyor sets at a property corner — most often a capped iron rod or rebar driven flush with or just below the ground, sometimes an iron pipe, concrete post with a brass disk, or a nail in pavement. Commonly called a property pin. Disturbing one is illegal in most states.
Modern monuments are usually 1/2- or 5/8-inch rebar, 18–30 inches long, topped with a plastic cap stamped with the surveyor’s name or license number. Older ones vary: bare rebar, galvanized pipe, concrete monuments, railroad spikes, or drill holes in curbs. They’re set at or slightly below grade, which is why a metal detector is the practical way to find them.
The flag, stake or paint you see after a survey marks where the monument is; it isn’t the monument. Flags vanish in weeks. The pin stays.
A found pin is strong evidence of the corner but not proof. Pins get pulled by fence and utility crews and re-stuck approximately, buried under fill, or set in error by an earlier survey. Surveyors verify a monument against the record and against neighboring evidence before relying on it; a homeowner’s check is measuring between two pins and comparing to the plat.
Removing, moving or setting a monument without a surveyor’s license is a crime in most states. Uncover it, note it, leave it.