When I press on some message to forward it, it shows me Random usernames of contacts I don't know. And it even shows some Mobile Numbers I don't know. For example, one number starts with +964 that's Iraq. I'm from Europe tho. These contacts and numbers are from all over the place.
Edit: This only happens on Signal Desktop. If I try to forward a message on Android it only shows my Contacts. And none of these unkown ones.
Why did someone see that I joined Signal?
People who already know your number and already have you in their contacts see that they can contact you on Signal. Nothing is sent to them by your Signal app or the Signal service. They just see a number they know is registered. If someone knows how to send you an insecure SMS, we want them to see that they can send you a Signal message instead.
Why did I see that my contact joined Signal?
You are notified when someone that is stored in your contact list is a new Signal user. If you can send an insecure SMS to a contact, we want you to know you can send a Signal message instead.
You can check that in the phone app too. Hit new message, enter the numer, hit "New message to... " and it'll tell you if it isn't known. There is rate limiting in that function, you'd need a lot of signal accounts to sweep all phone numbers.
You could also try signing up to signal using the number you want to check.
Neither way however you would get the signal name or profile pic of the number if I understand it correctly, that would get sent if they reply to you.
It's a necessary feature if you are using phone numbers. Signal has to tell you if your message has any chance of being received.
I don't want to message someones number, to find out they never got my message and don't have signal a few days later, and I don't want to message them via whatsapp too, giving them a chance to use that when they have signal.