What is the mon in Jin's kimono?
There is no way to know for sure, as it is not explicitly mentioned. While several other clans did use this design, the Takeda are by far the most well known. The four diamonds in this mon is said to stand for Takeda Shingen's famous, inspirational motto: "Swift as the wind. Silent as the forest. Fierce as the fire. Steadfast as the mountain," which was drawn from the writings of the Chinese strategist Sun Tzu (of "The Art of War" fame).

It should be noted that Yukimura bears the Houjou mon (looks like a Triforce),  who were neighbors of the Takeda and over time have been both allies and adversaries to them. Perhaps Jin and Yukimura's relationship in the show is a symbolic microcosm of the parallels between the real-life families?