This instruction was necessary - and in two colors. It designates a dial telephone rather than the candle-stick, operator-controlled telephone. Lift the receiver, flick the bracket a few times, wait for the operator, then say, clearly, “Union 9 8 2 2 1.” Wait. “Hi, Mom!”
Later, Ma Bell introduced the Touch Tone Phone. The tones made phone phreaking possible. The need to distinguish the phone pad from the dial became necessary. And now we distinguish between a telephone, land line, smart phone, mobie (UK) and cel phone. The smart phone is just a phone - the unmarked term. But we still dial. We have people on speed dial.
The dial interface is a body memory. The colonial prefixes - Union, Columbus, Hastings, Snelling, Marquette - is old rote learning from kindergarten.
All dials work the same way.