“policeman wearing shorts or jeans?”
Iv’e SEEN policemen in shorts. The shorts were part of their official uniform. This is common in many warm climates.
” Have you ever seen a soldier in the army shedding half his uniform just because he’s hot?”
The internet is filled with pictures of marines doing heavy grunt work in just their undershirts.
You dont need a reason to wear something if it identifies you as part of a group that you want to show your association with. I believe Rav Miller Z’l said he would wear a yellow (or was it green) hat if that is what identified him as part of the yeshiva crowd.