As with several of your knives, the mark is a merchant's mark. M. Klein & Sons is a distributor of mostly electrical supplies and tools. They have almost always sold variants of the TL-29 electrician's knife, and have purchased them from quite a few makers over the years. I can't get to my colelction of these right now, but yours looks to be Delrin, likely a Schrade, Ulster or Camillus made knife. Does it have a lock on the screwdriver/wire stripper blade?
EDIT: Never mind. I see the lock now.