We have symbols for everything but there is no symbol for "example" despite examples being fundamental to achievements.
Why is there no symbol for "example" when there are symbols for everything else?
I'd like to be able to write a formula and then have a symbol that is commonly understood to represent that what is presented is an example.
Why is this not a good idea and was not introduced?
For example:
E=hf
¤: f=3Hz... if we use ¤ as symbol for an example
I'd hardly say "we have symbols for everything".
The reason this is not a good idea is that the word "example" is not used in any context other than its natural language meaning; in contrast, "for all", "there exists", "implies", etc. are phrases which mathematicians want to use inside the mathematics, where the symbols $\forall$, $\exists$, $\implies$ come in handy. In fact, I (for one) generally avoid even using those symbols; I'd much prefer to write $$A=\{x\in X\mid \text{ for all }y\in Y,{\scriptsize\textit{ blah blah blah }}\ldots\}$$ as long as it isn't too unwieldly to parse.
There is no added benefit to having a symbol for "example"; using a symbol that serves no purpose other than to replace an English word, outside of the mathematical content of a discussion, just creates a barrier to understanding. I mean, if you want a symbol for "example", why not have a symbol for the word "remark"? Or "conjecture"? Or "bibliography"? Or "the"?