How to show/represent an ionic bond visually?
Some examples are as follows, 
$$
\ce{[Na]+ [Cl]-} \, , \\
\ce{[Mg]^2+ 2[Cl]-} \, , \\
\ce{3[Mg]^2+ 2[N]^3-} \, .
$$
Hopefully you get the idea, so a general rule is:
$$
\text{#ions}[\text{element symbol}]^{\text{magnitude of cation charge}} \text{#ions}[\text{element symbol}]^{\text{magnitude of anion charge}} \, .
$$