A great idea for purchasable cosmetics would be faction-specific name decorators. This way, players could showcase their individual favorite factions. They would be very unique and flashy-looking, and I think a lot of people would be interested in using them, and would pay money for it. My suggestions would be:
Iron Cross (German Army)
Hammer and Sickle (Soviet Army - this one could be a hammer in a side and a sickle in the other)
Star (US Army)
Rising Sun (Japanese Army)
People won’t pay money for meaningless random circles to decorate their names, but there is definitely no shortage of wehraboos and comieboos who would be willing to pay a few dollars for one of these. And before you say you don’t like them or find them offensive: so what? Make money off them instead of complaining, they will continue to be weirdos regardless of the name decorators anyway. Might as well cash-in and get some easily-pleased customers in return.