From Halopedia, the Halo wiki
The designator uses the same butt-stock, pistol grip and main section as the SRS-99D S2 AM Sniper Rifle, with the only difference being the absence of an ammunition magazine and barrel, and the replacement of these with a laser designator and different optical scope. The UNSC laser designator also has a Misriah logo on its stock, a feature retained from its SRS99D-S2 AM roots.
The laser designator was first seen in use in the Battle of Sector Six during the Battle for Earth, by an injured UNSC Marine Orbital Drop Shock Trooper, S. Hartley. After retrieving the package containing the designator from a combat zone with T. Rymann, the ODSTs proceeded to a position in Sector Six in order to acquire the trajectory information of John-117's descent through Earth's atmosphere. Though injured, Hartley succeeded in the task and the UNSC ground forces got to Spartan-117's crash site in time.
Visible on the side of the laser designator is the CE mark, which denotes compliance with European Union safety regulations. The "CE" is an abbreviation of a French term meaning "European Conformity". This may imply that the laser produced by the laser designator is not dangerous to any living human on its own.
List of appearances