Here are two Keen Kutters that I posted in the Counterfeit Watch thread over on the other knife forum. They were both ebay auctions, quite a few years ago, by the same seller. First thing that jumped out at me were the shields. I have never seen a shield, with such a fat bottom and narrow waist, on a Keen Kutter. The fact that there were two together, by the same seller, was suspect to me. The blades on both have been cleaned and buffed, yet, the tang stamps are, for the most part, quite clean and sharp. The tang lines all rise as they approach the backs of the blades. This can, not always, be a sign of a shaved and restamped tang.
One of the biggest flags, to me, is the spun pins. Neither knife has a pattern number stamp. In my research, the older knives, made by Walden, either had no pattern number, or had an etched pattern number at the top of the pile side of the master blade, near the tang stamp. I would expect the pins on such knives to be hand hammered, not spun.
Eric
ea42
also pointed out that it is very rare for a Keen Kutter sleeve board jack to have the pen blade, and it's nick, on the pile side of the knife (as it is on the second jack). I have since gone through all of my jacks, all of the photos in Sellens guide to Keen Kutters, and all of my ebay reference photos, and I would extend this characteristic to all Keen Kutter jacks.