Hi, Dan!
If the checkering is only scuffed with your fingernail, it's an easy fix:
Stockmakers normally use a small toothbrush to apply some oil finish to checkered areas. This can be tung oil (my favorite), boiled linseed oil, TruOil, Linspeed, etc. Furniture touchup oil (danish oil finish) would work too. A light touchup, let the wound absorb the oil, and then wipe off excess. That should do it!