Maru Mune
It doesn't seem like these are nearly as common, but perhaps my sample size is too small. When you encounter one, does it tell you anything different about the blade itself? Were they used for a particular reason? As a kantei point, on a mumei sword, should it lead a person in any direction, to a particular school or smith?
I found an oshigata of a unique blade with marumune, an Ohira-zukuri with a yokote. Made by Yosozaemon no jo Sukesada of Bizen. (the most skillful of the Sukesadas) According to the attached text it is unusual with marumune on Honba-mono, more common on Waki-mono. (Honba-mono, a center and well known swordproduction place. Waki-mono, made far away from such well known places)
But sometimes Marumune appear on Sue-Bizen blades.