I love Signal for a lot of reasons, but one aspect of it that is consistently frustrating (although I doubt unique to Signal) is how many times I get contacted by a stranger with a username that is nothing more than dash or a couple of dots (or even blank), with disappearing messages set to 8 hours or something. Only to find out later I've spoken with this person previously.
This becomes more problematic when the person reaching out is already somewhat nervous/paranoid about doing so (and in all likelihood has little experience reaching out to reporters).
My solution to this has been to start assigning aliases in my installation of Signal when someone reaches out for the first time. For me, aliases that refer in general terms to the topic at hand (not the person reaching out) have proven helpful, but I still probably miss a lot of good tips because sometimes I just can't be bothered.