How to designate a coordinate system

Question

Imagine I have a coordinate system where the coordinates are $a$ and $b$

How to designate this system?

$a-b$

$ab$

$a,b$

$aOb$ (where $O$ stands for origin).

Is there an accepted standard? I have never seen one.

Answer 1

No accepted standard, but most I've seen have been $ab$, that is, the two axis names without a space. A close second would be $a-b$, with a hyphen. I usually see that when the axis names are words, like "voltage-current graph".