There are only two kinds of relationships: Supporting and Opposing. Pause and think about that! Isn't it amazing that all the complexity we see in the world is built up from two simple structures combined in many different ways!
We denote the polarity by placing an "S" or an "O" by the arrowhead. We could also experiment with other notations eg I have used "only record the "O"'s and nothing by arrow = "S". I have also used a solid line for "S" and a dotted or dashed line for "O" relationships.
Variable X -> Variable Y
To assess polarity of this ask yourself if variable X increases in value what happens to variable Y. Does it go up or down? If it also goes up it is a supporting (S)relationship. If it goes down it is opposing (O).