[phenol]

I have never seen this notation used, but perhaps it is mean to represent steradians (the unit of solid angle)?

[chris_wot]

Not sure... But there is a Unicode symbol for it:

http://www.fileformat.info/info/unicode/char/299e/index.htm

P.S. thanks for the new term - steradians! It's amazing how many terms are in the mathematically universe :-)