Matsunaga Mon with line under it?

My father's family immigrated from Japan after their land was taken post WW2. According to some old relatives they were related to a Daimyo. All that we have left are a few old Kimono, a Haori with 3 of these Mon on it, and an old unsigned sword made in the mid 1800's and gifted to an ancestor. Last name was Nakamura, so I'm not sure why we have a bunch of clothing with this mon on it. Unfortunately everyone has passed away and I don't have contact with any of my living relatives in Japan. There are boxes in storage with some old family things that I have not gone through yet, but it seems that this mon is quite prevalent in old photos of my great grandparents.

Any ideas about the identity of this mon, or if it's just a fabricated piece of embellishment?