A yellow diamond-shaped sign generally means:

Yellow diamond signs are warning signs. They alert drivers to upcoming hazards or changes in road conditions: curves, intersections, road narrowing, hills, animal crossings, slippery surfaces, school zones, pedestrian crossings, and many more. The diamond shape combined with yellow background is reserved for warnings under the MUTCD, so the moment you see a yellow diamond you know to slow down and look ahead carefully even before reading the message. Some warning signs have specific symbols (a deer for animal crossing, an arrow for curves), and some have advisory speeds posted underneath. Advisory speeds are recommended maximums for the hazard ahead; they are not legally binding the way regulatory speed limits are, but ignoring them is unsafe.