I don't know what a console looks like, but I know damn well they can see if that voice channel is encrypted or not.
I'm running a couple of NXDN radios connected to a Zetron console. The radios are tied in via remotes to the console. The encryption is programmed into the radio and strapped to the specific talkgroup that the radio supports. The radio LCD screen will show the encryption icon.
But, the radio is in an equipment room, not the dispatch room. And there's nothing on the console that shows it's encrypted. I know for a fact that our dispatchers and most of the users don't know that I'm running encryption on some of the talkgroups.
As others have said, when setting up the radios, encryption often gets strapped, especially on trunked systems.