There are many 'sterile' SYKCO blades out there. Military overruns are one source of sterile blades, but I believe there were a couple production models that were never branded - DMCG, YG/YK? I have a DFCG purchased direct from Scrap Yard that is sterile, even though the first run (pictured on the knives page) shows logo present.

If in doubt, you can always ask here whether or not a specific model is known to exist in a certain configuration. Beyond that, while I haven't heard much about forgeries, but there is no substitute for paying attention to seller reputation in this game.