You can type characters a-z, A-Z, 0-9, and :,.!?)(" '-+=. I think they're all you might need.
Symbols, my carty uses are: ━┏┛┗┓┃┫╋┣︱┻┳ and ═╔╝╚╗║╣╬╠─╩╦ .
Some facebook symbols may not appear (showing up as squares, or ?) if the user doesn't have all the fonts required installed.
(some texts are only visibles in modern brownsers like Google Chrome o Firefox)
All this symbols also works in Twitter, msn, yahoo chat, etc.
To use, you must select with your mouse, copy (Ctrl+C) and paste (Ctrl+V) these symbols in your status messages, comments, wall post, etc.