I must have misread. Thank you.
No problem. That's an easy one to miss!
The hilarious side of visual signalling:
The light gun that is used is in the upper tower cab, usually mounted on a hangar near the window operating position. This position at a place like DCA is normally occupied by the ground and clearance controller(s). An air controller is also often up there to visually watch runway activity and aircraft on final approach or just taking off, but this can be simply the radar controller instead. He's on the floor below in a darkened room with no windows, so light guns are pretty useless to him!
The light gun signals themselves follow a short table. They are so rarely used, however, that both pilot and controller often forget what they are! I've used them myself (going into KMSP, or Minneapolis airport) when I had to take an aircraft in there that had no working radio. I can easily see in my mind's eye the tower controller going, "Oh shit! What's that light gun code again???". Fortunately, there's a little card next to the light to remind him. The pilot often doesn't have one handy! Students are taught these signals, but the memory of them fades over time pretty quickly, they are so little used.
The MSP controller handled it ok, but I could see he was a little unsteady on the light gun! He wasn't used to using it!
The reason for the NORDO approach (no radio) to MSP was that I was flying a busted aircraft to MSP to get it's electrical system fixed. While it was there, I also welded a hole in one of the exhaust stacks and helped to debug the electrical system fault. As always for such a flight, you call ahead to someplace like MSP to warn them you are coming without a radio. Cell phones sure make this easier!
It was sure nice to have a radio again!
During busy airshows, the 'tower' (often just a trailer sitting on the field somewhere!) is augmented by a couple of guys on the runway itself with green and red paddles to signal aircraft.
We have one airport here in Washington that uses such a trailer as the permanent tower! It sits BELOW the runway. He can't see the runway from the 'tower'! He simply watches the air around the airport and leaves planes to taxi for themselves (it's not that busy an airport!).
Another airport here has limited operating hours for the tower. They close at night, leaving the airspace uncontrolled.
Pilots simply announce their intentions to each other as they approach, land, or take off. Again, taxiing is up to you.
Y'all be careful out there!
