thank you very much for your answers!
I dont really know that much about the participation of my grandfather with the yugoslav volunteers but i know that he had anti-fascist and anti-communist ideals so i think there is a posibility.
I was asking about the badge being chetnik because my grandmother used to say that his husband supported the general Mihajlovic and that he was some kind of guerrilla fighter, they met in austria so i thought it could be that he was with the chetnik movement and escaped his country at some time during the war.
About the uniform being US or brittish i dont really know and never knew about contact with the US or brittish army.
The uniform also looks strange to me, i find the difference of colors between the hat and the jacket weird, i was told that he was once a police officer so you think it could be some knid of old uniform adapted for being a volunteer or chetnik?
thanks again for your answers!