In a collectspace.com forum, I found the following (merged) thread containing images, questions and answers: http://www.collectspace.com/ubb/Forum29/HTML/000962.html The two images below are intriguing as they use symbolic iconography.
Two posts from user
mercsim in 2011 say:
The characters represented a status between that station and the capsule. Reading like a book from top left, Command Control, Telemetry reception, Capsule Communications(air-to-ground), Radar, Reporting, Acquisition Aid, Ground Communications(Voice), Ground Telemetry.
The stations are fairly well published but it took a little digging to interpret the status symbols. (source: This New Ocean). An operator sat at a console (Network Status) and controlled the lights with a switchboard.
The information is actually in a table in Appendix G: "Ground Instrumentation Plan for Project Mercury." I found another slightly different version somewhere else. I can't remember the source but I have the table printed out in one of my nerdy reference notebooks. With a little detective work, I was able to piece the puzzle together.
I have a special interest in the original control center so it has actually been an ongoing project for me...
What is "appendix G" and how can I read these displays like a book to see the correspondence with the explained meanings?
These can also be seen in this image: