NORTH DIGHTON, Mass. -- Brand marketers can get in on the ground floor of in-store advertising by putting their message on tiles. Market Media, a subsidiary of BPI Packaging Technologies here, offers FloorFocus ad tiles that are laid on the floors of supermarket chains. Winn-Dixie Stores has signed up 1,200 supermarkets in the South. According to Market Media, trial installation of the floor tiles showed an increase of 15.7% in brand unit sales. Some brands showed a 58.8% increase in product movement compared with control stores.