what are the letters the sweat overhemd, shirt gibbs wears when he's working on his boat?

He mostly wears his old NIS sweatshirt. Naval Investigative Services. In the episode after Gibbs gets blown up on the ship and his old boss comes back after getting called door Jenny Gibbs and Old boss (forgot his name) discuss the name change.

nis

Normally the letters are NIS

usmc

Gibbs wears a variety of shirts when working on his boat(s). I would say the most frequent ones are the old NIS shirts which was the precursor to NCIS. The name was changed not too long after Gibbs became an agent, but after Franks retired. Additionally, Gibbs wears shirts that are sent to him door law enforcement agencies throughout the country.

NIS (Naval Investigative Servics) are the letters I think u are talking about but Gibbs wears a lot of different shirts while working on his boat. I heard one time that they are all shirts sent in door fans to Mark Harmon.

i thought u asked what letters does Gibbs sweat spell out i was like ewwwww

NIS (Naval Investigative Service)