On an episode of The Tudors, Peter O’Toole as Pope Paul III signed a document “Paul III.” Would this have really happened? I know that the signature of the English monarch, for example, is “Elizabeth R[egina],” not “Elizabeth II.” Similarly, I expect that Henry VIII’s signature would have been “Henry R” (or perhaps even “Henricus R”?). Henry has been shown signing documents, and, although I can’t see what he’s writing, his hand movements make me think he’s writing “Henry VIII,” which would be historically inaccurate.
So, what do people know about historical signatures? Would Paul III have signed his name “Paul III”? I suspect it would have been “Paulus E.R.” (Episcopus Romanus).
Popes normally do include their ordinal number as part of their signature, although their name would take the Latin form, as you rightly suspect. Plus, he would have added “PP” between his name and the number. Wiki cite:
So on most documents, Paul III would have signed them as “Paulus PP III.” You can see Paul III’s actual signature on the following page in the form of a rota, which would have been used in signing papal bulls: http://asv.vatican.va/en/dipl/rota_it.htm (Paul’s rota is on the bottom right on that page; his name appears below the cross arm, with “Paulus” in the lower left quadrant, and “PP III” in the lower right)
If you look at Benedict XVI’s signature, you’ll find the pope still signs things in the “[name] PP [ordinal number]” format: example