By ham standards, I'm far from being a long-time adept of amateur radio, but I've seen my fair share of shacks, both on the internet and in person.
What's always attracted my attention is that almost every one of them has some sort of platter with the operator's callsign on it in big letters, usually placed in a prominent place of the shack. And what's always eluded my understanding is the purpose of this.
The appearance in photos has the obvious benefit of telling the viewer whose shack it is, but it seems that most (if not all) owners of such platters keep them in the same place when not taking pictures.
Having a nameplate where your callsign is carved out of a block of wood, or etched in metal, or a nicely backlit acrylic sheet, or otherwise masterfully crafted might be simply cool to have around. But in a considerable portion of the shacks that I've seen the display is much simpler and cheaper than that. In fact, a lot of the time the callsign is simply printed on a sheet of regular paper which is then folded into a triangle so that it stands upright.
I know airplanes have such nameplates in the cockpit, but there it makes sense because the callsign is tied to the plane and not to the pilot, and it is common for pilots to hop between planes and vice versa, so it's a useful reminder what callsign you're currently operating. Similarly, I suppose it's quite useful in the case of special event callsigns, DXpeditions or other stations that have more than one operator. But once again this seems to be the minority, usually the shack is used just by the owner, and the callsign on display is their personal one.
Is there some other usefulness to this that I'm missing? Or is it just some kind of historical tradition that's still alive, and if so, where does it come from?
One of the answers states that it's a legal requirement in some places. Was it maybe a legal requirement in all (or at least more) jurisdictions in the past?