I appreciate you guys interest in my question. Here are a couple of shots of the machine in Harris tower, copied from the NRHS Harrisburg Chapter wiki presentation. The shot with the operator dates from 1938. The Harris Tower machine is much bigger than the one in Jersey Mike's avatar, (B&P Jct?)
For those who never worked one of these machines, the top row of levers control switches. With the lever leaning to the left the switch is normal. With it leaning to to the right, the switch is reversed.
The levers on the bottom are for signals. With the lever on center, the signal is at stop. With it pulled up to the left, it displays a signal in that direction, if the block isn't occupied. The same for the signal pulled ip to the right. One lever can control two opposing signals. The buttons on the machine below the signal levers enable an operator to get a restricting signal into an occupied block with the lever pulled up. On the Pennsy we call it a "hanger," or less frequently, a "call on," which is basically the same as the British terminology for it..