"Man working on Transmitter" Tag

[allnumbedup]

I think this object is radio rather than phone related. It is a VA-222F Varian Reflex Klystron Conduction Cooled Tube. The company appears to have been a early Silicon Valley outfit. The tag reads that it was removed from service in the late 1969. I think the tag is repurposed as this is not a switch but wonder if the tag is from a telco.

[G-Man]

Yes, microwave radio!
 
Klystron tube probably used at a telephone company microwave relay site. Varian/EIMAC are still giants in the industry.
 
Soon after WWII, Bell Labs and Western Electric developed for AT&T, a high-capacity, Coast-to-Coast microwave communications system that carried thousands of telephone calls and/or network television programs.
 
Here is an Wiki entry that provides a simplified description of one early system:

• https://en.wikipedia.org/wiki/TD-2

 
The tag alerted other techs not to energize the µ-wave transmitter while it is being worked on, so that the technician wouldn't end up having his cojones fried off or worse! Remember, Klystrons are still used in your home's microwave ovens.