There's not a lot to say about these. They were standard on every snare until the 2010 refresh, when they were changed to the square ones on all but a few special editions. 

Depending on the model, you'll find them both in a plain panel of the shell, and also through the badges -  especially the oval badges. They are usually screwed in from the inside of the shell so you can replace them if you wish - quite important in the case of a few Thomann specials which come with what some see as an unsightly removeable extra "badge".

Unlike the later square covers, there are no Black Panther models with multiple circular covers.