|The following is based on Fallout 76 removed content.|
The note could be found attached to the dome at ATLAS Observatory. To access it, one would go up the wooden staircases and follow the walkway facing northeast. It was removed with the Steel Dawn update.
I'm thinking about a big symbol, right on the front of the dome. Put a spotlight up there, aimed at it, so folks can see it at night. Really let everybody know the Brotherhood is here.
Have to do it myself, I think. I wouldn't trust the 'bots on these walkways. Maybe some kind of pulley system to lift it?