You can permanently disable your phone number from being recognized as a Signal user by unregistering your phone number.

Visit https://signal.org/signal/unregister/ or follow the steps for your platform:

• Android
• iOS

Android

1. Open Signal.
2. Tap on the Menu.
3. Choose Settings.
4. Tap on Advanced.
5. Tap 'Signal messages and calls' to slide the indicator off.
6. Choose OK.

iOS

1. Open Signal.
2. Go to Settings . 
3. Tap the red Delete Account button.
4. Tap Proceed to confirm.