I'm no expert but that looks like anything non signature does when it's stamped, uneven ink application, no extra darkness where the signature would naturally overlap, etc
I like your idea about the ink not being darker at the overlaps. Good point. Randi is 83 now and maybe does not like to mess with autographs through the mail. I have always resected the guy and wanted his signature.
Randi is a good guy. He has exposed many a fraud and many a charlatan.
If you send him a substantive letter about some of the scoundrels out there (Peter Popoff, W.V. Grant, Dennis Lee, etc. ) you might get a handwritten reply.