There are several Signature Electronic LED Signs for sale on EBay. I bought one that did not work and to get it working I had to add a power cord, and connect the 5 volt power to the processor board in the upper left corner.
The controller card has two wires that connect it to the outside world. One is green one is blue. I have traced them out to a "485" IC. That IC is a RS422 communications chip, so likely the sign is communicated with via RS422. You will need a Serial or USB to RS422 adapter to talk to the sign.
Here is what one of the Cadaces CDVO-1 boards looks like.