The Signature Verification Code gives you the opportunity to check the customer's signature before a transaction begins processing. It's not the customer's four-digit PIN.
The Signature Verification Code is defaulted to '0000', but we recommend you change this at the earliest opportunity. To do this, swipe right for the 'Settings' menu in the PayClip app, then select 'Security Settings'. Check that 'Signature Verification' is set to 'On', select a PIN and follow the on-screen instructions to set and confirm your four-digit code.