Guys,
both the broken circle and circled "U" go back a ways. I thought I had seen them on old charts so I dug out a few. Not my very oldest from the 80s, I don't know where they have got to, but...
WAC charts from the 1990s show _both_ symbols with the following descriptions in the legend.
Broken circle: "Unlicensed Aerodromes. Named in purple. Status and Serviceability Unknown"
Circle with U : "Aerodrome Landmark (unusable)"
It also seems that around 2003/4ish the description on the broken circle symbol on VTCs etc went from "Non Licensed Aerodrome (status unknown)" to "Aerodrome (Not Certified or Registered)"
Certifs.