Besides the virgule ("slash"), there aren't many glyphs that represent relationships outside of mathematical notation (including the Propositional Calculus), and none of them would be considered proper for use in formal writing. The ones you might see are → (becomes), ↔ (a reversible transition or an identity), ℅ (in care of), &, and @. There are a couple of others, like an overscored c, that are rarely included in anything other than professional font sets, that represent old manuscript abbreviations (the overscored c is "cum", or "with").
Even the virgule is only acceptable in certain kinds of formal writing, where the full expression in words would be tedious or awkward due to constant repetition. As jackgill mentions in his post, the meaning is ambiguous and contextual -- it can have the meaning of OR (and/or), XOR (one or the other, both not both) or opposition.
The backslash ("hack") is barely older than I am -- it's a child of computing.