I check a place's website when it's a grey area according to MI law. In MI, it's illegal to carry in an entertainment facility that has a total seating capacity greater than 2500 persons or on school property (special cases apply) whether it's posted or not, and in this case The Henry Ford Museum is a private educational institution and also may be considered an entertainment facility. It doesn't hurt to make sure.
Also, if someone is going to practice CANT they probably wouldn't be asking the question in the first place :dirol: