Nip-57 is the Nostr spec for zaps. Zaps are how your Nostr client knows when you get tipped and allows stuff like tip notifications, and seeing the number of sats tipped to a particular post. Both your client and your wallet that receives tips have to support NIP-57. Many are beginning to. So for instance the screenshot below is how Damus shows how many sats I’ve been tipped on that particular post.