Be aware that the font on the reader must have the symbol. Otherwise it will not be visible. The Symbola font is a very good collection of symbols/glyphs. On my site I have made a mapping from the Symbol, Webdings and Wingdings 1,2,3 to their corresponding unicode character. You can use that. By the way, the glyps on that page are from the Symbola font.
Mapping:
http://toxaris.nl/glyphs/symbols.html