Correct practice for representing units in figure and text? What is best practice (if any exist) for representing units of a quantity in figures and text for publications.

I have seen use of both () and [] for representing units, eg. in a plot if y axis represents velocity then v(m/s) and v[m/s]. 

I would like to know what correct: parentheses OR square bracket Or something else?
The publication likely has a style guide. Failing that, just flip through a few published papers until you find an example, then use that