Modifying a rotary ceiling fan dial so it can be operated by touch

My ceiling fans are controlled by wall dials. The dial has 5 positions - off,1,2,3,4 - and spins between them without stopping (meaning you can turn from off to both 1 and 4 directly, the rotation is never blocked). This has the usability issues that I must look at the dial when trying to adjust/turn off the fan, which is inconvenient, especially at night.

I've considered sticking some indicator (a small screw?) to the off position. But that doesn't remind me which way is 1 and which is 4.

How can I modify this dial so I can operate it intuitively by touch alone? Note that I don't want to replace it completely, just modify the existing dial somehow.