LEDSaid uses the asign library (https://github.com/tonymagro/asign) to send packets to Alpha LED Signs.

ledsaid -t "{SOT}{STX}{WriteText}{A}{Flash}{Red}Hello {Green}World{ETX}{EOT}"

This packet displays most features of the alpha sign protocol:
https://github.com/tonymagro/ledsaid/blob/master/demo/demo.txt

You can load a file served over http using the -w flag

ledsaid -w "https://raw.github.com/tonymagro/ledsaid/master/demo/demo.txt"