We operate a public nostr relay at wss://nos.xmark.cc. This relay automatically marks your nostr notes to the Bitmark blockchain, just like the Xmark browser extension does with the X/Twitter posts. For now the service is free, but of course, if in the future, block space becomes limited, then a fee may later have to be paid.
The Bitmark blockchain is trustless, decentralized, censorship-free, and persistent - A perfect place to store references to nostr events, and make it useful for people to search and find what what they want.
We also have a nostr account called 'Xmark Bridge' that forwards the posts made with Xmark to the nostr network. The public key is npub17dr8xyd5vy0tu7ejjg7284xtx3k4vlk4rfps3hp9s5v38zd42w4s5llnjh.