I was reading from Rayleigh's "The Theory of Sound" from 1877, and one of the first pages is dedicated to this signature which is given a proud position in the center of the page.
Can you summarize what the book says about the signature ?– EvargaloOct 27, 2020 at 16:04
The book does not mention it in a single word, the book is all about the physics of sound.. It is like, just there, right on the first page after the title page, with no explanation at all.– VinzentOct 27, 2020 at 16:05
2This leads me to suspect that it is a mark of MacMillian Co. Google image search for the win, although hat tip/FGW to @Evargalo– MCW ♦Oct 27, 2020 at 16:07
Looks more like a monogram than a signature.– TRiGOct 28, 2020 at 15:08
This image seems to be the signature of the editing house, the MacMillan company.
You can find other versions of their logo on their wikipedia entry.