Deniability though forgery doesn't really affect the traceability issue. If the police have good reason to think you originated a particular message they can ju

Deniability though forgery doesn't really affect the traceability issue. If the police have good reason to think you originated a particular message they can just seize your phone and do forensics on it. Chances are they will find traces. Failing that they can just find a single person who will testify that you sent them a particular message, which with forgeablity they can state with certainty. A prudent rumour mongerer would simply not sign the messages in the first place...