But the "observer" can still know which mobile phone is yours and who communicates with whom? Especially if the "observer" has the info from the Signal servers.

But the "observer" can still know which mobile phone is yours and who communicates with whom? Especially if the "observer" has the info from the Signal servers. Edit (as i can't post you reply to your answer): And based on the NSA principle of the "thee levels of distance" everybody is reachable as long as some common numbers are in our contact lists which we happily upload.