we discuss applications of the milnor-thom theorem, a result from algebraicgeometry concerning signs of polynomials, to the combinatorics of geometricconfigurations. in particular, we define an {it abstract lineconfiguration}, modelled on line configurations in $mathbb{r}^3$, and showthat there are many forbidden sub-configurations. we discuss theimplications for unavoidable "stacked" sets of lines via theerdh{o}s-hajnal conjecture, and pose several open questions. joint workwith uli wagner of eth z"{u}rich.