I think it may be for Naval Investigative Service .
[h=3]e plu·ri·bus u·num[/h]
The National Recovery Board label would date it anywhere from 1934 to the 1960's. Sorry, can't help you any more than that.
Thanks for the reply guys.
I know in 1966 it was called NIS(Naval Investigative Service ). I was thinking this but didn't know if the NIS wore uniforms or if they wore civilian clothes. But I would think the people who work in the office might of wore a uniform,and the people in the field probably wore civilan clothes. Never seen this insignia before.