Sniper Kill

From Halopedia, the Halo wiki

Awarded after killing someone with a sniper weapon.

The Sniper Kill Medal is a multiplayer medal awarded in Halo 2 and Halo 3. It is awarded for killing an opponent with a headshot using the Sniper Rifle or Beam Rifle in Halo 3, while any kill with either weapon will get you the medal in Halo 2. It is available in all Multiplayer gametypes where a sniper weapon is available and it is also possible to get this medal in the the Halo 3 campaign, with either of the sinper weapons and the M6G Pistol. Bungie difficulty rating of 1 (out of 10). It is represented by a six-pointed star with crosshairs. After you kill an opponent with a sniper weapon, a message appears on your screen that says: "You sniped (player)".