This key belongs to a Remington portable Model 5 from 1935, a very rare model that is very difficult to find. I love how flat these keys are and hoe well they fit on the holder, creating a unique ring shape.
What I like about the forward slash symbol (/) is that it serves to indicate line separations in poetry. The slash represents what would normally be a line break if the text was formatted using verse rather than prose.
In this key, this symbol with the coma gives a "musical" appearance as if it was some sort of symbol for a music chart.