The signature of <a href="https://en.wikipedia.org/wiki/Master_I._A._M._of_Zwolle" class="extiw" title="en:Master I. A. M. of Zwolle">en:Master I. A. M. of Zwolle</a>, 15th century Dutch engraver.
<a href="//commons.wikimedia.org/wiki/User:Lithoderm" class="mw-redirect" title="User:Lithoderm">Lithoderm</a>
CC BY-SA 3.0
Own work, Inkscape drawing based upon signature of Master I.A.M. in the bottom center of <a href="//commons.wikimedia.org/wiki/File:Mater_IAM_of_Zwolle_Virgin_and_Child.jpg" title="File:Mater IAM of Zwolle Virgin and Child.jpg">File:Mater IAM of Zwolle Virgin and Child.jpg</a>.