Edward Snowden is a public supporter and user of Signal. He's my canary in the coal mine. The moment the US three letter agencies get access to the data on Signal's servers, Snowden's dead. I feel comfortable in the resilience of their architecture as long as he's alive.
Do you think his location is some great mystery? The actual reason he is not dead is because there is no political will to conduct an operation on Russia soil to murder him.
Yeah, even if you believe the usa is full on evil, extrajudicially murdering someone who was granted asylum in russia makes very little sense from a political perspective given america's position in the world.