Servicemen in Vietnam often had souvenir uniforms made in-country from locally sourced South Vietnamese camouflage patterns (Another example can be seen here.). These souvenir uniforms were usually worn on leave to entertainment venues like movie theatres, restaurants, and bars (source: personal conversations with veterans), though a few were used in combat by Special Forces units. This shirt has a similar US cut as the Late War Lightweight Tiger Stripes. The camouflage pattern is similar to the “back” side of the Mitchell Vine Leaf camouflage shelter half and was mainly used by South Vietnamese Police Field Force (CSDC).
Patches appear to be original to uniform and have been attached for a long time.
Only marking is a red handwritten “8” on the back under the collar.