From Halopedia, the Halo wiki
Sniper Spree is a spree medal awarded in Halo 3, and Halo 3: ODST and Halo Reach in Multiplayer, Campaign and Firefight. In Halo 3 and Halo 3: ODST it is awarded for killing five opponents in a row with the Sniper rifle or Type-50 particle beam rifle (together or not) without dying. In Halo Reach the medal does not require kills to be consecutive, just that the player kill five enemies with a sniper weapon without dying.
It is represented by a steel four-pointed star with blue crosshairs.
The new remodeled version in Halo: Reach.