Well, certainly an anonymity flaw. Privacy is different than anonymity. Signal does not purport to provide anonymity. Anyone on the system can check for any oth

Well, certainly an anonymity flaw. Privacy is different than anonymity. Signal does not purport to provide anonymity. Anyone on the system can check for any other user by knowing their phone number. That tends to be the cost of the convenience of the automatic contact discovery provided by phone based messengers like Signal. Anonymous messaging is an entire category by itself. It is a much more difficult problem. Fortunately, most people don't need anonymity, most of the time. I really don't care who knows that I am communicating with friends, family or the people related to my business. If anything, I care less that someone might find out I use Signal. If I encounter a situation where I need to be anonymous I can and will have to take special measures for a while. Temporary anonymity is relatively easy. The identity management is a cinch.