KMKIII6 = K - Stainless Steel, MKIII - Mark 3 or third generation of Ruger's .22 pistol, 6 - Six inch tapered barrel with fixed sights.
My gun does not have the Ruger logo on the bolt, but once I had it scanned and digitized for the magazine base plate, I couldn't resist putting it on the bolt too.
Oh, a little history for those not interested in reading larger articles about this gun:
Bill Ruger's first .22 automatic pistol entered production in 1949. It was simply called Ruger's "Standard Pistol" and sold for $37.50. The barrel is made from steel bar and threads into the receiver which is made from steel tube. The grip frame is made from two sheet-metal stampings welded together in the middle. In 1950 Ruger added the Mark 1 Target model which featured micro-adjustable target sights. The Standard and Mark 1 target models were sold together until the Mark II came out in 1982. The Mark II's featured 10-round magazines (instead of 9-rounds previously), a bolt hold-open for when the magazine was empty, and little cutouts in front of the bolt's "ears" at the back of the receiver.
The Mark III's came out in 2004. Mark III's changes are: Moved magazine release from base of grip to button on side of grip (like most other guns.) The addition of a "loaded chamber indicator" on the left side of the receiver [which I did not include in my model 'cause I don't like it.] A magazine safety [another removed nuissance]. A safety lock feature which operates by key. Tapered bolt "ears". A slightly revised ejection port profile.