The differences are: * XMPP is using addresses with the same format as e-mail addresses (Jabber ID/JID), Signal accounts are bound to your phone number * Sign

The differences are: * XMPP is using addresses with the same format as e-mail addresses (Jabber ID/JID), Signal accounts are bound to your phone number * Signal has strong end-to-end encryption built-in, for XMPP you need OTR or the recent OMEMO port of Signal's end-to-end crypto magic * XMPP is federated, where you talk to your server, and it talks to your buddies servers; with Signal everybody talks to WhisperSystems' servers * XMPP has no decent iOS app, but pretty good multi-device support otherwise