I received more info about the 19-3 for those who are interested.you have a very rare revolver. this is what i found out.

Naval Investigative Service: In Feb 1966 the law enforcement and
counter-intelligence component of ONI was made into separate
agency, the Naval investigative service. An additional 200 of the 4"
round butt Model 19 revolver marked NIS with a yellow front ramp
insert, white outline rear sight and smooth combat triggers were
issued to NIS Special Agents. in 1972, approximately 450 revolvers
variously marked ONI,G2 or NIS were transferred to the FBI. A few
of these revolvers remained in service with the NIS and the FBI until
1990.

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The quick the steady the alive.