I thought that I’ve read one but can’t find it now.

For now the single at-sign can be placed using its html code … same with any special character. But I like the idea of a quick help link for these markup/special chars, same with link for supported smileys :)

Also, there should be some “escape” character, that voids the special meaning. Only a few people know the ASCII codes of the at-sign or the like out of memory – and looking up a table via google is not quite convenient.