That light is by the old Arc LLC company that shut down in 2006 or so (you can tell by the shape of the head, as others have mentioned). There were a few different configurations in terms of the location of the marking, and someone who kept better tabs on Arc variants could probably figure out the approximate manufacture date. I think the CS leds didn't appear until the later, reincarnated Arc. This light would have a BS led selected for good tint. The newest versions are quite a lot brighter, but people chasing brightness buy Cree-based lights these days. The light you have is a tastefully designed classic, that has some collectible value because of its scarcity, and is also a perfectly usable light just like it always was.