MLB Subway Sign with Field Dirt Seattle Mariners. This vintage-style Subway Sign is a must-have for any Seattle Mariners fan! Rather than showing the stops along a subway line, this unique sign details stops along the Mariners' history. Comes in a handsome black frame, and measures 1" Thick. Features dirt from Safeco Field, authenticated by the MLB! Guaranteed authentic by Steiner Sports. Materials: Mica, Plexi, Glass, Dirt.