Is there a to express certain values of a variable?
For instance, suppose $s \in \mathbb{Z}$, but there is an instance in which you are interested only in $s > 0$. I suppose you could write $s^+$, but I was wondering if there is a convention to follow.
EDIT. Sorry for the confusion. I have the following in mind. Consider a regression
$$y = \alpha + \beta s + \varepsilon$$
where $s \in \mathbb{Z}$. Now suppose we want to regress just on the values $s > 0$. I express this in writing, but I wanted to also distinguish this in the formula, like:
$$y = \alpha + \beta s^+ + \varepsilon$$
so the reader is reminded.