OK, I know that when you use a brand name it should be capitalized (do we also need to add the copyright © or registered trademark ® symbols?).

My question is, how do we know if a term is an actual trademark?

Some have slipped into common use and become just terms, like Linoleum, Velcro, Nylon, and such.

Others like Xerox (for copying), Kleenex (for tissue paper) and so on are on the verge of becoming everyday terms.

New ones are Googling. (I hate that term.)

I'm really wondering about thermos. Is that a tradename? Should it be capitalized?

For instance:

I noted that although they did not serve coffee in paper cups, they did have travel thermos mugs for purchase.

The only reason I was wondering is because I didn't know the plural of thermos and added the word mugs. Then I got to thinkin'. Always a dangerous thing.

Is there a website or something where you can go to find out about the use of trademarks?