I was told when the ccw law went into effect here in Ohio[about 1 1/2 years ago] that Walmart had no cororate policy against ccw.My brother works at Kmart here and it was up to the store manager if he wanted to post the "No Guns" signs.They are not posted at this time.As far as suing if they had signs up and you were attacked etc.Ohio law prohibits you from suing the store if it is posted. It also prohibits someone from suing the store if they are not posted and you get injured because of a licenced ccw's actions.They can sue the ccw holder but either way the store is immune to prosecution.Here is a link to Ohio's law.
http://waynecountysheriff.com/CCW_Booklet.pdf