Question

When must you sign a deposit slip?

Answer 1

If you are depositing a check or some money, You never need to sign a deposit slip that says "sign here if cash received from deposit".

As it says, "sign here if cash received from deposit"  that signing has to be in front of the Teller. So, if you are depositing your check or money  especially through an ATM, there would be no reason for you  to affix your signature...you're  not withdrawing, you are depositing.

Answer 2

I believe the answer is: B. You only need to sign a deposit slip when receiving cash.

Deposit slip would be filled with a list of cash and cash equivalent that you give to bank teller to be added to your bank account.
Most bank provide the services which allow you to take small percentage of your deposited check in the form of cash. When doing this, you need to sign it as a form of authorization.