Upon reading the Modern Method for the Boehm Flute, I came upon this notation:
What does the circle under the head of the note mean?
Take a look at page 19 of this PDF from the University of Florida:
It definitely seems to be an indication for a natural harmonic. I know @Richard said a harmonic was notated differently, but perhaps he was thinking of an artificial harmonic? As for the lack of centering, I can see that as a typesetting issue.
Believe it or not, I'm pretty certain this is just the worst-placed and worse-shaped piece of fuzz to ever find its way onto a scanner, because:
The nearest notation I can think of would be harmonics, but they are notated differently on a flute.