During the events of Making Money Moist von Lipwig is asking Mr Spools if he could print bank notes. Mr Spools replies yes, but there would need to be security measures to prevent forgery. He presents Mosist with a sheet of 50p green Tower of Art stamps handing him a magnifying glass.
“That’s top quality paper of course,” the printer said as Moist stared.
“You’re getting very good. I can see every detail”, Moist breathed, poring over the sheet.
“No,” said Mr Spools with some satisfaction. “In fact, you cannot. You might, though, with this.” He unlocked a cupboard and handed moist a heavy brass microscope.
“He put a lot more detail in than we did”, he said as Moist focussed. “It’s at the very limit of what paper and metal can be persuaded to do. It is, I declare, a work of genius. He would be your salvation.”

The are, of course, talking about Owlswick Jenkins.  When the 50p Tower of Art stamps were released, some extra higher detail Owlswick Jenkins forgeries were added to the LBEs. Here are the two stamps side by side; AMPO on the left and Qwlswick right. Click for larger image.

Ignoring the shade difference which could arise from different scannings, it is said that the best way to tell them apart is the point at the top of the dome. I also look at the weather vane detail. However when you see the full sheet, none of which were released to collectors, an easier method is available if the stamp has any selvedge attached. If there is any logo, official text, or printer’s guide marks then it is a standard AMPO stamp. If the selvedge is blank, has fingerprints, or contains any handwritten text then it is an Owlswick forgery.