English: Your signature here please.
French: Votre signature ici SVP.
Duty-free purchases may require the passenger to sign the receipt. You can hand them the receipt and a pen, saying "votre signature ici SVP."
Votre signature (f)=your signature
Remember the word for "receipt" is "reçu (m)". As you hand them their copy of the receipt, you can say "votre reçu, merci."
Want to learn to speak the French you need to work as a flight attendant? Learn even more with Canadian French for Flight Attendants.