is capital phi, the twenty-first letter of the Greek alphabet. It
is one of the letters in the Danish and Norwegian alphabets,
signifying a vowel sounding like a combination of the u in fur, and
the oo in foot. In computer notation it is the common sign for
zero. In the
mathematical theory of sets it means the empty set.
In other contexts can mean diameter, and in still other average, mean, in which case it is semiotically connected to the Chinese use of . See the entry above.
As a biological sign it has been used to signify a dead female (a combination of for nullified or cancelled, and for female).
Compare its use here with the use of below in this group. Compare also with the very similar sign , for Ares, the Greek god of warfare and aggressive action.
Turned, like , the structure appears in the US system of hobo signs with the meaning a good road to follow.