A card, currency, and/or bill denoting a return or refund.
Examples:
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I believe the bottom would represent well with MD. I have labeled it as cash-usd-refund.

This looks excellent!
We use the standard credit card icon to denote payment. Could you foresee a use case for a hybrid of the card and the "undo" circle like you did with the cash-usd symbol?
After discussing it with the contributors, we've decided not to use the USD sign. So I've created one for cash return and card return. Thoughts?


Could also use the left one for cashback/rebate and the right one for refund.
Some inspiration:
In my online banking, they use this icon: 
For transactions they use this: 
I think the cash return and card return icons are great!
Most helpful comment
After discussing it with the contributors, we've decided not to use the USD sign. So I've created one for cash return and card return. Thoughts?
cash-usd-refund.zip