[ATP]

That it's printed onto the image (or stamped), manufactured facsimile signature. I'll post the ones I have later and you can compare, it's probably easiest since you can see your in hand, I'll try to get good scans of mine.

edit: Found an old photo I had saved of a couple, hope this helps. The postcard is a JD McCarthy from the sames series as your I believe. Note that the tail end of the signature looks cut off on the one you have.