A sign on which the canopy can be changed, either manually through the use of attachable letters (usually plastic) or electronically using incandescent bulbs or light emitting diodes.

A sign that includes provisions for message changes. Also called changeable copy panel, changeable copy sign, time and temperature sign, electronic message center, menu board.

A variable (also changeable, electronic, or dynamic) message sign, often abbreviated VMS or CMS, is an electronic traffic sign often used on roadways to give travelers information about special events. Such signs warn of traffic congestion, accidents, incidents, roadwork zones, or speed limits on a specific highway segment. They may also ask vehicles to take alternative routes, limit travel speed, warn of duration and location of the incidents or just inform of the traffic conditions.