It needs to be done in a text box... holding a complex expression.
Because I don't want to evaluate the result (number; postive or negative) twice (one for getting the sign, and one for displaying the actual value) I wanted to use a formatting option (if available).
Hope this makes things a bit more clear.
I think Florian was able to supply me what I need.
All solutions where '5' was put more than once in the expression might have been good, but I wanted to avoid evaluating '5' multiple times (as '5' should be replaced by a complex expression in reality).
Thanks to all for your very fast responses!