• But... I remember the VMS prompt being "$"... maybe some ancestry since VMS dates back to 1970?

VMS development started in 1975.   It didn’t see the light of day until the VAX hardware was released in 1977.

RSX used > (sometimes MCR>).

TOPS-10 used a period (.) at the monitor level and asterisk at the user level.

RT-11 also used the period.