Reference Marker
A reference marker is a small green placard displaying a three-digit number that’s placed at intervals along all state-designated routes in Texas. Reference markers are used by TxDOT and the Texas Department of Public Safety as general reference points as ways of identifying locations of vehicle incidents or roadway work being performed. Reference Markers do not describe mileage along a route.
Illustration: Reference Marker installation guidance.
Photograph: Reference Marker on the roadway.
TxDOT Visual Dictionary