I see no reason to use the term safety switch. Disconnect switch is much more useful.
A “disconnect switch” can be any number of devices, a safety switch (in this context) is a specific type of disconnect switch.
The Square D story, for those who never heard it, is that the company was originally called McBride Manufacturing Co., but started making fuses, so changed to the "Detroit Fuse Manufacturing Co." based, obviously, in Detroit. But at the time, fused switches were, as mentioned, the open knife switches, like in the Frankenstein movie set, where anyone walking by and brushing up against the conductive parts could be shocked or killed. Ford wanted something less dangerous for their new assembly lines and since they were using Detroit fuses, Ford came to them for ideas. Detroit Fuse enclosed the knife switch (at first in a cast iron box, but by 1915 it became sheet metal) with a handle to the outside to operate it.
The idea was wildly popular. Detroit Fuse put their logo on the front of the box, a "D" for Detroit, in a square box, to represent the enclosed aspect of it. But over time, people just kept referring to them as "them switches with the square and D on 'em". Eventually that became so much more important to their business than the fuses, that they sold off the fuse production and changed the name of the company to The Square D Co. (and later, just Square D).
1921 advertisement;