If all you want to do is write characters to it you don't even need the serial smart board, you can do serial output with just the digital out pin. The sign is an RS232 device and if it adheres to the RS232 standard it may require a higher signal voltage than the 5V the ioBridge provides. There is a chip called a MAX232 that boosts 5V signals to RS232 levels, you can buy them on ebay two for a dollar.
In terms of programming: IObridge has widgets that allow you to send serial messages to the serial outputs. The spec sheet doesn't say anything about how it is controlled, I assume you have to mix control characters in with your message. You'd probably want to make up a simple javascript program to send control characters and messages.
