The Rules Blog
We have all found a golf ball or two whilst looking for our own and frequently they’re in mint condition – occasionally there are two identical balls in the same proximity (Thank you for the Klinger Sponsored – Srixon AD333 No.3s on Reddings) The point is that they are often totally unmarked and therefore NOT Identifiable.
Rule 6.3a – Holing out with Same Ball Played from Teeing Area
The player should put an identifying mark on the ball to be played.
Penalty: Surprisingly none, but how are you going to identify a ball in the jungle if it doesn’t have your personal mark on it and will your opponent in match play accept it’s yours if its not marked.
It’s a simple task and definitely in your own interests.