I have read of individuals who learned to roll their hands in such a way so that one motion would complete a signature and neatly land the signet ring in the wax. This is for people who have to sign and seal a lot of documents, which leaves me out.

I believe signet rings have followed fashions. I have one with an entire achievement of arms- shield and crest- which is too big to wear on the little finger. It is intaglio carnelian and yes, the image is reversed. The stone is oval, but is roughly the size of an American penny. The original owner received it in 1919 or thereabouts ( Wally, fifth Earl of Lough Leif) and it passed to me about 50 years later. I have another which would be a generation older, which is bloodstone, with only a shield, no crest or torse. It is roughly half as large and fits nicely on the little finger. Maybe Wally had no taste, but I believe his ring reflected one of several troughs in popularity of the pinky ring.

Another periodic shift is from the shield to the crest as subject. Like a set of initials, one crest can belong to several people, but there is also the general notion of understatement- why use your whole name if a monogram will do?

Some of my friends still find pinky rings highfalutin , so when I am passing the pint of Inver House, I tuck that finger under.