Hi 25B, We may not be on the same page. I have a lot of pull the dot caps. Not sure that's the correct name because I have heard numerous names for the part that has the pull the dot printing on them. I looked at mine thinking I lost my mind and didn't see the mark your talking about. None of mine have a mark on them.
I was at a fellow saddle maker who uses these and he has a die that the cap fits in and when you press the corresponding part to the cap it puts a small dimple on the top of the cap. I looked at his die and on the inside is a small pimple that marks the cap. I just purchased a sizable order with Index and they have the die and Ohio Travel bag has it also.
If the above information has flaws in it please educate me. Thank you, and also I appreciate your feedback. Don't ask questions you never learn.