I have open carried at the Lowe's in White Lake, West Bloomfield, West Lansing, and South Lansing. Never had an issue at any of them. I had a conversation about firearms with a store manager at one of them, while I was carrying. He carries a Kimber and was interested in what I was carrying.
I bought appliances and flooring and had plenty of interaction with staff. If firearms are prohibited at Lowe's, it will be news to me and their staff. If there was a sign at a store, it's store policy, not corporate.
Interesting to note, Home Depot prohibits recording devices in their stores.