From what I read in an old thread at the Schrade Knives Collectors forum, I would guess that the 501SC is a drop point hunter with scrimshaw that came out in 1979, but I am no expert on this, you may want to ask over there, I believe a picture would help.
I think Don Luis is right on the money with the identification, if your knife looks like this one. The base pattern was the 154OT Drop Point Hunter. 1979 was the only year that I am aware of when this pattern was used on the Schrade Scrimshaw Series, though a variant pattern, the 158OT Guthook Skinner was used much later on several issues. By far, the small fixed blade pattern most commonly seen in the Scrimshaw Series is the Sharpfinger.