Didier, thank you for your reply and your link to a most interesting website of French prison staff uniforms.
The five pointed star is used by many countries, but the wreath of fine leaves stands out. I think I have found it.
https://www.vietnamwarcollectables.c...-vietcong.html
It is a North Vietnam shoulder board button, used by the army and navy.
It also fits with the contents of the tray.