Absolutely tell them, but in truth if they said "please don't do that" you would remove their name - so I'm going to state it as I did originally (edited for clarification) - Absolutely ask them.
When you are faced with questions such as this throughout your life, which you will be, it's good to have a foundation or base (I dare to leave morality off of this response but it does feel natural to call it a moral base but I digress) that keeps your actions in line with who you are and who you strive to be as a human being.
In this case, you are concerned about asking for one reason or another. It appears it's not something easy for you to do and as it may never even be noticed or come up beyond this one letter there's a certain logic of "why even do something difficult if it may not matter at all".
You do it because it's the "right thing" to do and your stomach knows it. I did put "right thing" in quotes as it's often phrased as such in colloquialisms but please don't take that as a denigration, it really is the right thing to do and I'm in no way mocking that. The stomach or gut reaction to things in life is actually extremely important and not given it's place in our decision making as the quantification of such feelings isn't established and thus we incorrectly assign it a lower value than what it does in fact represent in terms of importance, use and overall big picture frameworks for building a better society and self.
You wrote this post because it is nagging you. If something is nagging you, address it. It's very simple. If what you are doing to address the nagging isn't negative, hurtful or damaging to yourself or others then the nagging must be a concern that NOT addressing it could be just those things - hurtful, negative or damaging at some point in the future.
Your concerned you may be doing something "wrong", something that goes against who you are and who you want to be in this world as a person and your writing of this post is a perfect example of that concern which isn't necessarily at the top of mind but more subconscious if you will.
Good people ask these questions and seek these answers, so my respect to you for asking and taking responses.
This may read as over assured or single minded in a way, and the single minded part can partially be supported I'm sure, but it is intended to be an open and honest response using the philosophy and method I have come to respect and try to apply in my own life - nothing more.