The REGISTERED SIGN (®) was introduced in 1946 with the Lanham Act. (In
Section 29.)
Quoting from:
https://bitlaw.com/source/15usc/1111.html
"..., or the letter R enclosed within a circle, thus ®;..."
There was no mention of it being superscripted. It would be interesting
to see a scan from the original. It would surprise me if it appeared in
the original document as a superscript symbol.
In this PDF from the U. S. Patent and Trademark Office on page 237 (from
January 1, 2023),
https://www.uspto.gov/sites/default/files/documents/tmlaw.pdf
... the symbol is shown in running text at a normal size and on the
baseline.
Seems to me that the organization that invented the symbol should be
considered the authority on its display.
