So we have this 11th century hymn, “Ut Queant Laxis”, in which the following seven syllables fall on the rising scale from the tonic, i.e.:

Ut Re Mi Fa Sol La Si = CDEFGAB

The lines in a stave indicate the notes. If C is “Ut”, then the second line from the bottom in the stave is G, or “Sol”, so let’s write a “G.s” on that line.

Over time, “G.s” = 𝄞