A messaging device (100) has a keyboard, keypad or other input device (150) that receives entry of a message. A processor (110), upon receipt of a command from the keyboard (150) instructs the messaging device (100) to append a signature (which might be or have a graphical content) to the message, executes a program process (200) that determine how much unused space is available in the message (216). The program then selects (220) a signature, from a plurality of possible signatures (170, 172, 174, . . . , 176) having varying size, that will fit within the unused characters and appends (224) the selected signature to the message.