They only need your sig in the event you dispute charges.
Cs’rs pay with card from time to time at the restaurant, take both copies and call in and dispute the charge. Guess who doesn’t have a copy and has to eat it.(reimburse)
Let me share some things. I worked in a big bank in BDU (Billing Disputes Unit) and in Fraud for 8 years. Its been a while but I doubt much has changed.
Yes then bank will issue a Chargeback for UNAUTH TRAN and ask for the media (charge slip). And you not having it does not mean you lose at all. You represent for plastic at POS (Point of Sale) and ask if the account was closed L/S/A and on what date (Lost/Stolen/Altered). If it was not you win. If it was it goes to fraud and the bank has to write it off.
Talk to your accountant. Chargebacks for UNAUTH TRAN almost never stick unless the acct is in fraud then its a w/o on the issuer.