Exit Number sign
Gives the exit a number that usually matches the nearest mile marker rather than a simple running count from one end of the highway.
Mounted in the upper corner of the main green exit sign, or as its own small marker on the shoulder just before the ramp.
How to recognise it
This sign is a square in green, used only for directions and distances. Green for directions, distances and exits. They never tell you what to do, only where things are, which is the simplest way to remember the colour.
What the test wants you to know
New drivers often expect exits to run 1, 2, 3 in order. On most interstates the number is the mile marker at that exit, which is why exit 24 can be followed by exit 31 with no exits 25 through 30 ever having existed.
Practise it
Reading about a sign is not the same as recognising it in half a second with an examiner watching. Every state road signs test on this site shows the sign and asks you to name it, then shows four faces and asks you to pick the right one.
Interstate Route Marker
US Route Marker
State Route Marker