What is the right sign to show in a retail shop

Solution 1:

Neither form is free of sin; a more-proper form is:

If you would like a receipt, please tell cashier.

Here is a scenario suggested by the second sign, which says, "Please ask cashier if you would like a receipt":

Customer: Would I like a receipt?
Cashier: Let me consult my crystal ball.

Solution 2:

Both forms mean exactly the same thing but would be better written as

Please ask the cashier if you would like a receipt

or

If you would like a receipt, please ask the cashier.

This suggests that a receipt would not normally be given unless you request for it.