Sketch is/was a Standard Phase 1 Clone Trooper who was assigned to Battalion Sergeant Slick's platoon in the 212th Attack Battalion.Very little is known about Sketch, and has only appeared on-screen in the Clone Wars episode "Hidden Enemy".
Sketch wears Standard Phase 1 Clone armor, while his facial appearance consists of having a "high-fade" haircut with long sideburns and a letter "S" tatoo written in Aurebesh on the right-side of his forehead. (To distinguish himself from other Standard Clone Troopers.)
Sketch is one of the very first Clone Troopers to have sideburns. (Aside from Punch and Jester.)
Star Wars: The Clone Wars "Hidden Enemy"
Star Wars: The Clone Wars Character Encyclopedia
Star Wars: The Clone Wars "Shadowed" web-comic