Is the text sent from my number or an unknown one?

It's sent from a number dedicated to your business at Signal, not from your line — technically, a phone can't text itself after a missed call. That number stays the same for your entire subscription: every customer who calls back or replies finds the same thread, not a string of disposable numbers. You can have your regulars save it under your business name, and the sender label is set at activation per your country's rules. What your customers see: your name as the first word, not a six-digit code.