Port Out PIN
From VoIP.ms Wiki
The Port Out PIN is a 4 digits number that protects your DIDs against unauthorized port out requests. By adding a PIN to your account, the port out requests need to pass and match this number for them to be authorized.
The Port Out PIN option will only apply for selected US numbers containing the lock icon.
The port out PIN option can be found in the customer portal by going to Main Menu > Account settings > Security Tab.