Official Target Policy was... if the signature panel, is not signed... and the transaction was suspicious, a team member could ask for additional identification (such as state issued id/driver's license)
Technically, we're not allowed to ask for a driver's license, if the signature panel is signed. It's against Target's merchant agreement with the credit card networks (Visa/MC/Amex/Discover).
I'm not sure if that's still in effect or not. But... we ran with it, quite a few times at my store. 😉