He then informed me that it was a courtesy to tell an officer if there is a weapon within reach.
Wait... I'm confused. You told him it was within arm's reach - under the seat. You extended the courtesy that he requested.
Ah! But the information was not volunteered without prompting. There is the rub.
By claiming it is a 'courtesy,' the officer wants you to feel obligated to preemptively inform him about information that you did not have any legal responsibility to inform him about when he is in the process of dealing with you on a professional legal manner. Hmmmmm.
Lots of things are a courtesy. Saying "yes, sir" and "no, sir" are courtesies. Addressing him by his rank and name are courtesies. By chance did he try to educate you on any other parts of etiquette? No, because he really isn't interested in courtesy. He is interested in a misguided perception of officer safety, that he needs to know about weapons present by law abiding citizens and to assess you accordingly in case he may feel threatened by you.
By chance, did the officer inform you of the weapons he was carrying? Did he extend you a similar courtesy? I bet not.
I had an officer in Texas that was unhappy with me for not informing him fast enough that I was carrying. He approached the vehicle, identified himself, said he was pulling me over for speeding, and that he wanted my license and insurance. I had my license and CHL in my hand and was handing them to him as he was finishing his request (trying to be efficient and courteous to the officer) when he got somewhat upset that I had not first informed him verbally that I was carrying a weapon. To have done so would have meant actually interrupting the officer during his spiel (again, I was beign courteous and letting him speak without interruption). While you have an obligation to inform the officer in Texas, the exact timing and method of informing the officer are not stipulated by law. For some reason, he just wasn't happy that he had my CHL while he was speaking and before words came out of my mouth to inform him. Go figure.
I have no problem with informing cops that I carry. As I have met several cops over the years (lead footed driving), numerous times I have gotten the response back "This is Texas. We assume everybody is carrying."
Quite interestingly, we can now carry in our vehicles without license and people carrying in their vehicle that don't have a license have no duty to inform...which is why the apparently removed the penalty for not informing officers.
If you want to inform the officer in a state where informing the officer is not a legal responsibility, that is on you and it is something that can be helpful to the whole tone of the traffic stop, unless of course the officer is one who feels like citizens should not have guns and then things may not be so helpful. Getting informed/chastised/or lectured for something you are not legally required to do is nuts.