What is the proper way to address NCOs in different branches?

Back in the day - 1990's - when I was a Gunnery Sergeant, shortly before I retired, a sailor on board the USS Nassau called me "Sarge" .... I leave it to your imagination as to the response - and he was a Senior Chief.....

If your looking at a senior NCO, it's by Title. But if your looking at E4-E6, the naval ranks (Coast Guard and Navy) are the most difficult since they don't have a rank like Sargent. Instead they identify rank by position. So if they are a cook you'll call them one thing, and if they are a cryptanalyst, you'd have to call them something else. A simple what of addressing them is calling the Army, Air Force and Marines as Sargent and the Navy and Coast Guard by Chief until they correct you. Then call them by the title they tell you to address them by.

Also remember, there are two other services, US Public Health Service and NOAA. These services don't have enlisted, but their officer ranks are the same as Naval Ranks. You should address them as such.

You address an E-7 in the Marine Corps as Gunnery Sergeant. There is no other officially authorized term of address. Unlike in the Army where you would call an E-7 Sergeant in address and Sergeant First Class or Sergeant when talking about them in 3rd person...

Address them as Gunny Sgt., MSgt., Chief (Air Force, Navy, Coast Guard), etc.

Lol, you call a Marine E 7 properly as Gunnery Sgt, especially being out of unit. You know him he’s Gunny.

MC E7 is Gunny, I’ve never heard of anyone ever getting bent about that.

I was Army stationed on an Air Force base one of my boss' was a gunny.

The DoDI (50110-04-M) has the way to address each rank of each branch. The Salutation for a written letter corresponds to the service etiquette of verbal address.

https://execsec.defense.gov/Portals/34/Documents/511004m_v2.pdf?ver=2013-03-02-045134-443

By their rank!

Marines: Full Rank, according to MCO 5060.20. It wouldn't be a bad thing to call him "sir" out of politeness unless he's extremely salty. Gunny and Gunnery Sergeant are preferred forms of address for the GySgt.
Army: SGT - MSG may be addressed as "Sergeant" or by their full rank, according to AR 600-20.
Air Force: SSgt - SMSgt may be addressed as "Sergeant" or by their full rank, according to AFI 36-2618.
Navy is a little different. Petty Officers from 3rd through 1st class are referred to as "Petty Officer" or by their rating ("CTR1" for a Cryptologic Technician Receiver 1st Class Petty Officer). Chief, Senior Chief, and Master Chief Petty Officers are generally referred to as Chief, Senior Chief, and Master Chief respectively. The Coast Guard, PHCC, and the NOAA, since utilizing Naval Rank structure (though some do not have enlisted, like the PHCC and the NOAA), follow suit.

I would say By Short Tittle...

I’ll admit I was in the wrong in the following situation.

I had to go to al Assad air base in Iraq to train some marines. Cool fine whatever. I had an e-7 marine talk to me and I said Roger sgt. He then tried to chew me out and force me to call him gunnery sgt snuffy. I said Roger sgt. If he would have been polite and respectful, I was an nco and in the army, I would have done things differently

The E-9 Marine told me to just call him Top. I said that works for me.

For the Navy it's Petty Officer then Chief, Senior Chief, and Master Chief.

Just do what I have always done. I ask them what is their rank. It has worked well.

So, fun story. I’m a Marine that has switched to the Army. My last rotation we had a Marine unit stationed with us and my LT was the middle Man in dealing with them. This guy would constantly come to me “SGT Baswell, how to I talk to Marines” “ SGT baswell, why when I saluted a Captain in the field did he look at me like I had a dildo attached to my head”
It was fun to watch..

Also on the flip side, I came into the Army with no “welcome to the Army” OSUT or anything just arrived at fort hood grabbed a uniform and poof soldier. So SFC comes and asks me a question, and I accidentally called him gunnery Sgt. And was looked at weird. Definitely takes some getting used to with the culture shock

In the Old Marine Corp, Cpl's are to be addressed as Sir by all other branches of service in the world. For example: Marine Cpl, "Are you eye ****ing me?" Everyone in the world, "No Sir!"
Have a great Marine Corp day. I'm having one.

As a former US Army NCO and having worked with all branches, fall back onto what you were trained to do. When I worked with USMC Recon at Onslow Beach, Camp LeJeune NC we addressed the company gunny as SGT. His having done joint training before, he expected it. His marines about lost their shit over it though.

I do have one good statement as a Sergeant First Class (E-7) I was at an U. S. Air Force Medical Center and the Tech that called me up and called me as a Senior Specialist. So at that I corrected the individual. He was very happy to informed of the correct rank.

I work as a civilian in a Navy facility where there are both active Navy and active Marine personnel working daily. The Marines are very particular about it and expect to be addressed by their full, correct rank even by civilians. Don't take shortcuts there, even an E-3 in the Marines will be insulted if you get it wrong or don't use it because they feel that they earned it.
All the other branches I have worked with are much more laid back and the Air Farce is almost like being a civilian with regard to rank. They really do call each other by first names.
It is best to use the rank until you know how the individual feels about it.