In US English, "sign off " usually means something unrelated to signing a contract. We would write, "Please sign the attached contract." "Please find attached the contract for your signature." "Attached is your contract. Please sign."

Please & Kindly at the beginning of the sentence are confusing, you should only use one or the other and I would suggest that Please is the best for this context. You would use Kindly to ask someone to do something, such as 'Please find your contract for sign-off, kindly return it to me when you completed it.' As for Signoff, it is two words, not a single word, so either use 'sign-off' or 'sign off'.