I appreciate your comments, but that doesn't really match up with the known facts. Laura's mother's name was Nancy Gray. Nancy's parents were John Gray and Sarah Gustin, so there's no Martin there. None of the other known Gray children in the family had a surname as their middle name, and after Nancy Gray married Thomas Hendren (about 9 years after Laura's birth), none of her subsequent children had a surname as their middle name. So while I agree it could be possible, I don't think it was likely because it would appear it was not customary in the Gray family.
Anyone else, PLEASE!