serial headers... any clues?

My project is moving right along with a PCB designed for the 595 shift register matrix display driver. However, I seem to have hit another wall and was hoping for some suggestions. I will be sending display data to a small network of arduino boards and want each display to be separately identifiable… as far as I understand, this would mean using a header at the start of the serial data to identify which display should be receiving what display data… I can not begin to sort out how to do this on the arduino end (host software just needs to send an additional header byte yes?). Does anyone have any suggestions or informational links?