English: The notorious 'Bembo M'. French printers and typefounders of the 16th century apparently idolised the work of Venetian publisher Aldus Manutius to the point of copying an asymmetrical capital 'M' in his 1496 book De Aetna for many years.
This example is shown in a book from 1556, Vascosan's printing of the mathematics textbook De Rebus Mathematicis. I do not know the details of who made the type, if this is even known. Shown above it is a modern digital font 'M' in matching style (the font is ET Bembo) which is symmetrical.
It seems reasonably certain that Manutius's 'M' was an accidental glitch caused by faulty typecasting, since his later book Hypnerotomachia Poliphili (same lower-case but with new capitals) has a symmetrical M, in the tradition of Roman capital letters.