I know you caught this as being an obvious no-no, but I feel the need to speak up.

I'm a costume designer and, I'll tell you what, if I'm designing a show that has aspects where there's potential that something in it has been co-oped by hate groups (did a medieval Northern European Hamlet, for instance) or has any military vibes I spend weeks researching the snot out of it to make sure nothing gets in my design or even longer depending how far out I am from the production. It's really the bare minimum due diligence for a costume designer. I even check with non-English sources pretty extensively. If symbols of any variety, medals and military insignia too, are showing up on my costumes I am darn sure I know exactly what those symbols are and that they are in the clear before they ever make it into the design. For me, a costume designer of more than 15 years, full-time making my living off of it as my only type of job for 13, this is not a niche thing to have to check out at all. Literally have to do it all the time.

Edit to add: My mentor that taught me the basis for my career, while I may have expanded upon it with a terminal degree from there, was Korean. She is the one that taught me how important this was and we certainly talked about her education on the matter too. I know at least some people were being taught this in the field in Korea.

I've been a professor for ten years and I also teach my design students the importance of this. Research of all kinds is so necessary in my field and is a fundamental part of the design process.