Any (?) debit card can participate in credit transaction. Either you chose Credit option on pin pad or indicate it otherwise (press enter key without entering pin at some groceries). This will be signature transaction. Many businesses just default transaction to credit type - coffee shops, fast food.

If one is lazy enough to enter pin, he can chose/request credit (signature) transaction at most retailers and cases. IF POS (register) allows such type of transaction for particular purchase.

WM money related transactions are not allowed to be of credit type, we all figured.

As of Emerald we don't know yet, whether switch trick will be required...