Who do we address as First Sergeant?

First of all there is no such thing as an acting 1SG. If a SFC is set in that position then that is exactly the duty he/she is performing. You would address them as 1SG because that is the title they hold while doing the job! I also held the position as a SFC, however like someone else already commented there is no acting your doing the job. If you chose to hold that position and are weak and let your soldiers call you sergeant because you are acting then that’s your malfunction fix yourself.

The Air Force also has First Sergeants, they can be anywhere from E7 to E9 but nothing lower ever in today's service. In all cases they ARE the First Sergeant. They report only to the Squadron Commander. (unit on level with Company in the Army or Marines) As an E8 I have held the position of First Sergeant twice and very much enjoyed the job. It was made specially good by having a great NCOIC in the Orderly room and great clerks working there and a great Commander !

I think this is a very good question and some very good answers. I still even as a First Sergeant address MSG by their full title. I know that the regualtion states that you don't need to do this, but to me they are in the same grade as myself and should deserve the same type of respect. As for the SFC thing, if they are filling in the role of a 1SG, I still call them "Sergeant", being that they have not been selected by the Army to the rank of First Sergeant/Master Sergeant. I understand the CSM placing them in that position, but why? Was he/she just the best of the lot, were they really that good? There are a lot of different variable, and I think you have to feel it out. I mean no disrespct to any SFC's serving in a First Sergeant position, but to many of us, we had to endure a lot to get to that postion in our careers and I feel due the respect that comes with the rank. Just one First Sergeants opinion, do with it what you will.

Since this is a Customs and Courtesies Class. Can someone dial me in on TOP being a rank. I must not be tracking.

The history of being called Top or First Sergeant has been ingrained in the army history for decades.  It refers to the TOP NCO in a Company.  By regulation, All NCOs from E5 to E8 are called Sergeant even Master Segeant, period.  But we often hear Master, or Sergeant First Class, or Staff Sergeant.  For me, It does not matter if my Soldiers call me First Sergeant or TOP.  I believe they are showing the same respect to the rank.  As for filling a role a grade higher than you hold, you should addressed at the rank you carry not the rank of the position.  As others have stated, your NCOER will reflect the position. Just my 2 cents!

I've actually never, EVER, used the term "Top". I've combed through regulations and I've never seen that in the rank structure. It's like referring to your Command Sergeant Major as "CSM" when you reply to him/her, I've also never done that. Sometimes the guys in my unit will poke at me about it, but I don't care, it's giving a respect for a rank earned. For me, it's always "Yes First Sergeant" and "Yes Sergeant Major". I also address MSGs as "Master Sergeant", I just feel like E-8 is such a great accomplishment that you should give the respect of the rank. I point this out because I see a lot of people who will bring up topics about SFC serving as a 1SG and saying "Well he's not a 1SG so I don't call him that". But you're the ones who use "Top", and that's not the rank that a 1SG is either. If you're gonna be right, then be right all the way. You can't pick and choose when to be right based on convenience.

I feel as if the SFC is in the position of 1SG, then I address them as such. Conversely, I have had occasion to work with some fine individuals that have given up the diamond. These few I still refer to as 1SG out of respect for the job they have done. Both of these groups have earned the right to be called First Sergeant or Top (depending upon your unit).

With all due respect to everyone who is saying that a MSG should be called Master Sergeant, please read AR 600-20 it's in Black and White and any individual serving in a capacity other than what they normally would be serving in, should be referred to by their tittle, unless they are being referred to by their Rank for PAI, UPL, EO or any administrative action. 

I never use the word TOP when addressing a 1SG ever. Sounds to much like slang  to me.

I would say if a SFC was assigned the duty of 1SG, he/she would be called Sergeant. I have many NCOER's with rated time as 1SG but was a SFC. I preferred to be called Sergeant. I do not know the book answer, just my thoughts.