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

For Marines:

E7: Gunny or Gunnery Sergeant
E8: Master Sergeant or First Sergeant (has a diamond in their chevron)
E9: Sergeant Major (always), Master Gunnery Sergeant or Master Guns if you know them.

For ranks above E6, never call them Sarge or Sergeant. Just sayin.

Until notified otherwise, address them by their rank. BTW, Marines call E-7 Gunnery Sgt or Gunny, not Sir.

Horse shit! You do not ever EVER address any enlisted , no matter the rank!
Cpls, Sgts, and staff Sgts are addressed by rank. E-7s (gunnery sergeants) are called "gunny"
Msgts are known as "top" ( as in, top sergeant)
Retired from the Corps I still CRINGE at being "sir"

Mow that the Army wears the rank just below the target line, the one that gets me is the 1st SGT and SM. The difference between the star and the diamond are too damned small for anyone with "aged" eyes.

Never had that much trouble with the stars over the anchors due to locations. But he Diamond and the star are in the same SMALL place.

Just my $0.02.

Marine Recruit training is a strange animal. Because Recruits are not considered Marines they are expected to show the upmost respect to those who already hold the title and that is the only place an enlisted Marine is referred to as "Sir." Long story short, all enlisted are called by their ranks. E-5 is Sgt; E-6 is SSgt; E-7 GySgt or just Gunny; E-8 MSgt/1stSgt; E-9 MGySgt or Master-Guns/SgtMaj. Gunny and Master-Guns are the only acceptable nick names and sometimes a MSgt and a MGySgt are referred to as "Top," but most don't like that name, a 1stSgt or a SgtMaj should never be referred to as "Top" I know the Army does that sometimes.

Marines do not address NCO's as Sir/Ma'am. They address them by their rank. The only exception is recruits. While in recruit training, recruits address their NCO drill instructors as Sir. Under any other circumstances, addressing a Marine NCO as Sir/Ma'am will draw you a highly negative response!

If you were seeing Marine recruits (not graduated from boot camp yet) they address everyone ass sir, ma'am. The rest of the services are addressed by their rank. I had to teach my wife (Air Force) all the ranks of all the services before she went to Air Force basic. It used to be part of Marine Corps recruit training to learn these things....dunno anymore, graduated in March 1995

It is appropriate to address members of other services by the rank and our last name (if known). If they are actual recruits, have not yet graduated boot camp, they address everyone by sir or ma'am. But, during boot camp, they are taught all of the different ranks of all of the different services so they can address other service members appropriately.

This may have been said before in one of the responses but the actual PROPER response is by rank, and last name (if necessary). That is (IMHO) the safest way as well - as how familiar one can be with a person of superior rank is dependent on the person and his or her mood in any given moment - as I learned one night from a sergeant with whom I thought I had a pretty good relationship with hanging out after duty hours. One night in a bad mood and PO'ed at our CO and he decided to take it out on me. It was a hard lesson.

The guy was WAY out of line and I was told by our First Sergeant, who heard of it I could have had his stripe but the guy had ten years in; two tours in Nam, and personal problems. It wasn't right, but I also realized I owed him a debt of gratitude for teaching me a great lesson about being too familiar with those in authority over you. From that time on I have NEVER addressed a supervisor by his or her first name - no matter HOW close we might become; and I've never found myself in another situation like that night in Germany.

JMO - learned from experience. Now there are titles and nicknames that are generally accepted. Last names for enlisted personnel were okay when I was in, Sergeant -----, passed for NCOs, First Sergeant - "TOP" was an honor when I was in but I understand it has been a no-no... rank for officers, but when in doubt I don't think you can go wrong with rank and last name.

All enlisted personnel in the Marine Corps are addressed by their rank. In the case of an E-7 he/she would be addressed as Gunny. Every Gunnery Sergeant I have encountered will allow that nickname. And by the way, E-5 is Sergeant. NOT sarge.
The only time I was ever required to address an enlisted person as sir was while attending boot camp.