I feel your pain. In my house I have many panels with multiple switches. In one location I have three 2-ways, two 3-ways, two hot outlets, one switched outlet, and a pilot light. I often stand there and flip sundry switches until I get the result I need. And I'm the person who wired it.
There is no widely recognized vocabulary of symbols or colors to indicate the information your users need. Even if you try to label all the switches with descriptive phrases, how are you going to unambiguously refer to the various loads and locations?
"Kitchen Lights" -- OK, but there are three separately controllable sets of lights in the kitchen.
"Kitchen Can Lights" -- Did your cat write that? I know they can light, but how?
"Kitchen Lights West" -- Great, now I need a compass. Which I couldn't read anyway because it's f'k'n dark in here.
"Hall Outlet" -- Look down that hall. Seriously. Just count the outlets.
"Upper Half of Second Hall Outlet on the Right" -- Now we're looking at "goofy" in the rear view mirror.
I didn't label my switches with words because no one in my house can agree on what anything is called. And my family already has enough "goofy" to deal with in this 130 year old ark.
I have allowed a little bit of nerdy goofiness into my design: I added color to some of the switches.
My cover plates match or coordinate with the room colors. All the switch levers match their cover plates. All the constant-hot outlets match their cover plates. No semiotic coloring there.
Where I added color is in rings around the switched outlets and some of the switches. In the shop and craft room, where slightly more garishness is allowed, the color is applied to the entire outlet or switch (except the lever).
I applied the same color to all the switches in each multiway group, with each group having a distinct color. Similarly, each switched outlet half shares a color with its switch.
There's only a few colors I like, so I re-used colors where there's no possibility of confusion, such as on separate floors. Going through the Pantone chart to insure absolutely unique colors throughout the house ends up looking kind of "goofy".
This color coding sometimes helps me remember which switch is which. I think it helps others in the house too, but they'll never admit it. They all like to pretend that it's "silly" and "overkill" and "lame".
And no amount of colors and symbols can make my biggest panels easy to use. I still have to flip switches until I get the result I need.
I think you'll find that the real problem is not coming up with a working label scheme. The real problem is that whatever you develop, you will have to explain it to an impatient and unappreciative audience.
