I'm not understanding the question. You can set up a table and create a field of type File Attachment, and upload any image, including an image of a Signature. That can then be used to display on a form.
"<img src=" & URLRoot() & "up/" & [_DBID_where the image is stored] & "/a/r" & [Record ID#] & "/e10/v0"
& "\" width=\"200\">"
On the example above, the image is stored in field ID 10