On a drive through Amersfoort you see eight signs: a round white sign with a red border and the number 50, a yellow diamond, a round white sign with a red border and otherwise empty, a round white sign with a red border showing a red and a black car side by side, a round blue sign with three arrows in a circle, a round blue sign with one white arrow, a triangle with a red border and the point upwards, and a blue square sign with a pedestrian on a zebra crossing. From how many different categories of the sign classification do these eight signs come?