What's the unicode glyph used to indicate combining characters?

Question

My application needs to display "orphaned" combining characters. I would like to use the same format as the "official" unicode charts, using the dotted circl

Answer 1

I don't think there is an official placeholder character. The way I read that note, they chose U+25CC arbitrarily, purely for display purposes. Then, in the chart where the "real" dotted circle is listed, they made it a little larger to emphasize that it's not being used as a placeholder there. (Or maybe they shrunk it in the other charts; as you said, the note's poorly worded.)

Whatever the case, I don't see any reason not to use U+25CC as your placeholder.