This is a simple class I wrote to communicate with a 1990-era Betabrite led matrix. This should serve as a decent start for other led signs using the Alpha protocol.
See http://www.teksolutionsllc.com/download/alphaprotodoc.pdf for the protocol documentation.
You need also a serial interface that recognizes TTL level signals and a RJ12 cable and adapter. In my case I got the link working wiring RJ12 blue to pin 5, red to pin 2 and green to pin 2 and using MiniPiio v0.20 RS232 interface with raspberry pi 2.
My sign is model 1040 with firmware "1040-4402 EZII". It seems to have some problems on the hardware side of things; a) the clock doesn't update at all on its own b) some text modes crash the sign (flash, slot machine) c) the sign doesn't advance on the run list from file to file unless they are either on rotate, condenced rotate or twinkle modes (probably realted to the rtc problem).