Yellow A-Board Warning Signs. Our yellow safety a-board signs have been designed for strength and stability. Manuactured from bright yellow lightweight moulded plastic to ensure the sign is clearly visible. Each yellow a-frame has curved ergonomic handles for added comfort when carrying the sign and folds to save on storage when not in use. The hinge restricts opening to ensure maximum stability is achieved on this portable, folding safety sign. Yellow safety signs are an ideal way to ensure safety around the workplace and in your business, you may need to advise that the floor is wet or the door has just been painted and what way to do it than with a professional, economic yellow a board.