Interstate Route Marker sign
Identifies which interstate highway you are currently on. Odd numbers generally run north to south and even numbers generally run east to west.
Federal designation M1-1 in the MUTCD, the national standard every state signs to. Posted at every interchange and repeated every few miles along the route so drivers can confirm they are still on the correct highway.
How to recognise it
This sign is a trapezoid in blue, used only for motorist services. 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
Three digit interstates are the real exam trap: a number that starts with an even digit is usually a bypass or loop around a city, while one that starts with an odd digit is usually a spur that dead ends into downtown. Examiners test that pattern far more often than they test the shield itself.
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.
US Route Marker
State Route Marker