ISO info abt Naval Prison Detachment uniform

[Lightech]

I recently learned my great grandfather was a private in the Marine Corps during WWI. He served from 7 Nov 1918 to 19 May 1919 at Mare Island, CA in the Naval Prison Detachment co D. He received the Sharpshooter Medal and Good Conduct Medal.

 

Im trying to find any uniform decorations,emblems, insignias he may have worn on his uniform.

 

Was there a specific collar pin or shoulder patch to distinguish he was in the prison detachment?

 

Side question: What would have been some of his duties?

Thank you for any information.