If you click on "Settings" at the top and then "Users" on the left hand side as below you should see this page:
If you click on the user for whom you would like to add a signature, then you should see this page and the area where you can add a signature. To upload the signature, click 'Upload file':
Select your signature from your saved images on your desktop. This will upload. Click "Save" at the top of the page:
This signature can be added to all letters and prescriptions.