From User Jordan Miles Hamanaka Kaplowit's comment to this question: Meaning of samurai crest / symbol
What is the meaning of the sixth crest symbol?
That appears to be a
maru-ni-mitsu-kashiwa (丸に三つ柏) crest, also known as a
maru-ni-makino-kashiwa (丸に牧野柏). It is an encircled, three-leafed version of the
kashiwa crest designs, one of the Big Ten styles of crests. These crests features an underlying design derived from the leaf of a Daimyo Oak tree.
In Winter, dead leafs of a Quercus dentata tree do not fall until new ones starts to grow in Spring. Thus, since ancient times the kashiwa has symbolised the continuity, or the propagation of the family through generations . These are appealing elements in Japanese culture, which has historically placed great importance on perpetuating familial lineages.
As is usually the case with the more plain designs, the
maru-ni-mitsu-kashiwa has been used by many clans. The most closely associated is probably the ancient Makino clan, who even lent their names to the crest. But several other families used this too, including the
Nagae, and the
Kuriyama. One notable user was Shima Sakon, a retainer of Ishida Mitsunari. He was famed for being hired with a ridiculous salary (half of Ishida's land's income), and for fighting with ferocious bravery in the fatal Battle of Sekigahara.
In addition, there exists a huge range of different
kashiwa crest designs. Here are some examples:
From left to right:
mitsu-kashiwa crest, an un-circled version used by the Kasai of Mutsu.
maru-ni-tosa-kashiwa (丸に土佐柏) crest, thinned version used by the Yamauchi of Tosa
tsuru-gashiwa (蔓柏) crest, a veined version used by the Unomiya Shrine (鸕宮神社)
daki-gashiwa (抱き柏) crest, used by the
Hiromine, priests of Hiromine Shrine
chigai-kashiwa (違い柏) crest, a crossed version used by the Kanou of Ichinomiya Han
(I'm only naming one as an example for each; in fact there could be dozens more different clans/shrines using the same crest.)
Moreso than samurais, however, the
kashiwa designs are as a group very popular among Shinto organisations, including both the shrines themselves and priestly clans. This is due to the Daimyo Oak tree being historically regarded as a holy tree; its large and study leafs a traditional (and literally green!) food container for making offerings to the gods.