It doesn't run on the OG Tor network itself as I understand it - people run their own specific Session Nodes that act as the "tor-like" backbone.

The crypto part is because to set up your own node, you proof of stake a bunch of their coin, and if your node is found to be unreliable or blatantly malicious your stake is locked (or even forefitted? Not sure about that part)

I did a similar contact card thing for (real) people I cared about from Discord. 2 people installed signal to keep up. 20+ invites went out before I nuked they account. One person already had signal. The other one that installed it now ghosts all my signal comms attempts.