Stop Sign
MUTCD R1-1
Come to a complete stop; proceed only when it is safe.
What it looks like
A red eight-sided octagon with a white border and the word STOP in bold white capital letters across the center.
When you'll see it
Posted at intersections without traffic signals, at the end of many side streets, and wherever cross traffic has the right-of-way.
What to do
You must come to a complete stop at the stop line, crosswalk, or corner, then proceed only after yielding and confirming the way is clear.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.