1. Both displays use the same old (circa' 96) control boards made by LightLink / Inova
2. Controlling board has a 10baseT interface (multiple ports)
3. When light up + connected to a router, both signs display an IP address information
4. Port scanning returned nothing.

after a quick google search i found that these screens connect via UDP - but no luck finding the packet format / protocol

I`ve decided to rebuild the controller board using a simple PIC + ESP8266 combo and write my own protocol for the display