Stop and No Passing, for two

ROADSIGNS

Think of what drivers obey that includes both a red octagon and a yellow diamond.

This clue plays on two common traffic signs: "Stop" and "No Passing." The phrase "for two" hints that you're looking for a single term that covers both signs, which is "road signs." The answer combines the idea of multiple signs into one word, making it a straightforward but clever way to tie them together.