Looks like a form of Lichen. try rubbing it with a scotch pad but wear a dust mask.I picked up two sticks off the ground yesterday in the same general area so they may both be from the same tree, a sugar maple. They both have these spots - I'm color blind, so I'm guessing they are gray.
Good grief, I can't speil eather.
Can anyone here identify what this is and and suggestions other than chipping away with my hand chisels.