I posted the following last year.
"I regularly find halves and other coins with one thing or another put on them by sharpies or similar markers. I find it annoying. A few years ago I ran into a coin counter bag that had over 200 coins marked. Three of these were significant errors. A 1974D Doubled-Die, a Bicentennial Cud ('76D if I remember right), and a major die crack. I find the practice of coin hunters marking coins to be a sign of abject stupidity that cost this coin hunter about $100 in lost revenue in just one bag."
My latest annoying find, a few months ago, was an old Jefferson nickel with a repunched mint mark. The letters "RPM" were on the reverse. The coin, a 1942D over horizontal D, would likely have graded about 55, but the marking, even if cleaned, would degrade the value by 25% to 50%.
Personally, I do not care what anyone's reason is for marking coins they have searched. It is still a sign of if someone that is operating on "The Not So Bright Side".
I would continue, but it is time for more coffee.