It’s a purple check to verify that your name is legitimate. You register with a service like nostrplebs.com so no one can steal your exact name. The people hosting make a small upfront fee. Not sure the long term economics of it. nostr:npub18ams6ewn5aj2n3wt2qawzglx9mr4nzksxhvrdc4gzrecw7n5tvjqctp424 would have a better answer to this.