Kalmykia a country within the Russian Federation, issued a pane of stamps featuring eight female rockers. I assume the 5.00 refers to five Rubles; but it can be five sweet potatoes, five Bud Lights, or whatever.
For those who prefer, there's the Mariah Carey stamp. And some others.
The world of postage stamps is an odd one. First, there are some places that get a lot of revenue from postage stamp collectors, like Pitcairn Island. (Or the island's 50-60 residents have really humonguous letter writing habits.)
Then there are some out-and-out fake places issuing postage stamps, like the notorious ones issued by the National Socialist Croatian government in exile:
But these are totally fake, so you need not look for them in your mail.
But Kalmykia is a real place; the only part of European Russia that is largely Buddhist. These may be locally issued stamps, or they might be fakes.
It's nice to know that other places have their priorities set right.