What is red rectangle at front of viewfinder?

I can't find any reference to the red plastic part at the very front of the URSA viewfinder (looks like a car indicator). Is it for sending communications between the camera and the viewfinder?

That is the Talley light, used when the camera is connected to a ATEM and may come on when the camera is recording, if you set this in the menu. This gives the taken an indication of when the ca era is recording, and in a multi-camera switching situation, which camera is being used.

The Viewfinder (EVF) communicates with the camera is via the SDI connection, which also carries the video signal.
Cheers

Thanks for the explanation.