Bonded Aluminum Signs Bonded Aluminum Signs are printed onto Aluminum Panels that are attached to a plastic core.Available on 3mm Aluminum Metal Sandwich Board Prices are Low at Costello. Save more money on you outdoor metal signs. Save with store pickup here in Sacramento. INSTANT PRICES - ON SIGNS POPULAR SIZES:12″x12″18″x12″24″x18″24″x24″24″x36″36″x36″Custom Sign Sizes Available.