It is the mortgagor who is in charge of signing the promissory note and the mortgage. The promissory note is usually given when the mortgagor is unable to pay the required amount yet. By signing this, he proves that he will be able to pay the amount eventually. There are some that come with dates that need to be followed so that the promissory note can be accepted.
Just remember that the time will come when the promissory note will not be considered anymore especially if there are many months that have passed since the time when the payment was supposed to be received. Mortgagors who are unable to pay the mortgage may be in danger of losing their homes.