I'd try maybe a dab of alcohol or household cleaner first.Another option is to get a can of goof off paint remover, dab a little on a Q-tip and try to remove one little spot. Don't press too hard or you'll go through whatever finish is on the cue. If that small experiment spot drys ok, then do the rest. I would try it. Worst case is you screw it up and then need to send it to Proficient.
Mark the blem on the blank or stock.Doubt if it's a marker. The darker area begins and ends exactly at the edge of the points. They were there before the cue was assembled.
What some call blemish, others call figure.
Enjoy your cue.