I pulled these Siemens DL 2416 from an old PBX. They are seated into an 18 pin right angle adapter that reduces the size down to the standard 0.3 inch wide pattern. I found the datasheet for these online.
Each character of the four character display consists of small segments of red LEDs. There is a decoder on the display, so it’s just a matter of feeding the display characters. More on this in the datasheet (PDF)DL2416T.
I did a Google search for it and I saw something about this display and Arduino, so check out the search hits to see what’s out there. Maybe there’s free software out there for it.
Seems that nowadays no one wants to mess with LED displays because they are power hungry compared to the LCD displays. That’s true, but the LED displays can be used in line powered equipment without being detrimental. Obviously we can’t compare these to a full color LCD display like we find even in the cheapest cell phones. But they can display a good set of characters – see the datasheet. Two of these have a total of 8 characters, but the characters can be scrolled in software, so a whole line can be displayed slowly.