# Is it possible to denote "any single alphabet symbol" in an FSA state diagram?

This is a possible duplicate of the following (but not sure it answered my question):
Is it possible to support .(any symbol) or \d, \w, \W in DFA

My professor is asking for a finite automata state diagram for some language that accepts even length strings (actually it's more complicated than that, but I'm starting with that as a subset). But he didn't define the alphabet of the language (on purpose). We can assume the alphabet is definite, but I assume I can't just use an arbitrary alphabet instance.

Here is a DFA/NFA state diagram concept that I think accepts even strings (including $$\epsilon$$):

But what alphabet symbols / terminals should I put on the edges? It shouldn't be $$\Sigma^*$$. It shouldn't be $$\epsilon$$. Can I use $$.$$ ? Can I use a $$*$$ ? Can I use anything as long as I describe what it means?

EDIT - I just found the use of $$*$$ in these notes of an Illinois course (p.4):

"." is a poor label, since it's too easy to miss. "*" is a confusing label since, in regular expressions, "*" means "any number of times", not "any symbol". Since it's quite common to see arrows in automata labelled, e.g., "$$0,1$$", I'd probably label the arrow "$$\sigma_1, \dots, \sigma_k$$" and note in the caption that $$\Sigma = \{\sigma_1, \dots, \sigma_k\}$$. Or you could just label the arrow "$$\Sigma$$".
• I like your suggestion, as it leads into the formal definition as well ($\Sigma$ is defined formally). Feb 4 '19 at 16:31