If you prefer to have a signature captured whenever making Notes, navigate to Forms then click the Note tab at the top right. You can either create a new Note Form or edit an existing one.
Once you have opened the Note Form, click + Add at the bottom, or the + between existing fields
Select the field called Signature
To force users to sign before they can submit, toggle the "Required" option to on
Select "Add item"
Remember to Save & close.