Inlays C613000 6" x 6" 0M MM Series Smooth Ceramic Tile Waterline Depth Marker with Centered 4" Black Lettering on White Tile, Frost Resistant. We offer the most extensive line of depth and safety markers available, including products for new construction as well as renovations. Our tiles are printed with ceramic glaze inks, then kiln-fired to ensure the finest, most durable depth and safety marker line available!