n? h?

It's the astrology symbol for Saturn. Probably part of an astrological dingbats font.

Under which key?

I don't think there's an accepted convention

P in Astrology 1
http://www.fonts.com/font/monotype-imaging/astrology/1

0 in Astrology 2
http://www.fonts.com/font/monotype-imaging/astrology/2

4 in Astrology 3
http://www.fonts.com/font/monotype-imaging/astrology/3

H in Astrosym
http://www.myfonts.com/fonts/paratype/astrosym/regular/


See more of the same here

Unicode: U+2644