This of course assumes that your business is following sensible security practices, such as not sharing logins/passwords.
If you'd nevertheless prefer to have a signature captured whenever making Notes, you can add it to the bottom of an existing Note Form or create a dedicated Note Form for this purpose.
See below for how you'd go about this.
Navigate to Note Forms, and either create a new Note Form, or click to edit an existing one.
Click to add a signature field to the form where you need it to be
The field 'type' that you'd be interested in adding is called "Signature". See below:
Change the label and mark it as required if you'd like to force a signature before saving can happen, and click Add item:
Now click Save & close: