No idea on the marking but it's on the tail boom of a U.S. Army UH-1 Huey Helicopter or possibly an AH-1 Cobra Helicopter. Tee shirt and stencil name looks early to mid 1980's. It might be marked for use in an Opposing Forces excercise.
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United States Army Republic of Vietnam (USARV) was a corps-level support command of the United States Army in the Vietnam War. The command was created in July 1965 to control support and logistical units for the Army combat units in Vietnam.
The 520th provided aircraft maintenance and support during the years 1967 and 1972.
Don.....
USAF '63-'69
Nice work!
Here's a nice depiction of a 520th Trans Huey with the Unit Patch on the nose. The aircraft, Huey's and Chinook's used the "Pipesmoke" callsign for aircraft recovery missions.