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