It means what it says. The current speed zone is null and void and it's up to you to figure out a safe speed to drive until you encounter a speed limit sign again.
A motorist is expected not to drive faster than the speed limit on the sign until the school has been passed.
When it is flashing the speed posted is the limit
No passing zone!
It means that you are about to enter an area where the posted speed limit is lower than the one you are in now.
In North America this is an Advisory sign.It can mean "warning corner" or dead end or similar.ORIt can advise you that Playground or school zone that is not allways a reduced speed limit.
A square yellow speed sign is not a Speed Limit sign, it is a sign listing the advised speed limit for that turn, but you are not required by law to be going that speed or under while going around that turn.
As soon as you pass the sign. If you are in a 65 MPH zone and it changes to 55MPH, you are expected to be at 55 MPH at the sign.
I'm assuming you mean the 35 MPH sign that has a yellow background with black lettering. These signs you'd sometimes see below school zone signs, off/on ramp signs, corner signs. This sign suggests a speed where you can take the obstacle ahead safely. The sign is saying "35 MPH is a safe speed which you can take this obstacle at". Being a suggested speed sign, if your judgment says you can take the obstacle faster, then you can, it isn't a speed limit sign.
Pedestrian crossing or school zone
The school zone sign indicates a reduced speed limit, typically 20-25 mph, when children are present or during school hours. Drivers are required to slow down to ensure the safety of students crossing the road or walking near the school.
An orange sign typically indicates a construction or work zone when driving. These signs are used to alert drivers to potential hazards, changes in traffic patterns, or the presence of road construction activities. When encountering an orange sign, drivers should exercise caution, reduce speed, and be prepared for altered road conditions. Following the instructions on the sign helps ensure the safety of both drivers and construction workers in the designated work zone.