Thanks guys - The question came to me as a result of calibre's recent support for half star ratings as in
I assumed the full star was Black Star (U+2605) and the half star was - good question. I assumed it was hidden in a corner I couldn't see.
Maybe Kovid has pre-empted acceptance of Ken Shirriff's proposal and he's using the HalfStarDemo.ttf - that might be it, the timing fits. He's had a lot of requests for half-stars.
BR