[pas]

if I put a stop sign somewhere is that legal? or there's some statute (or at least local ordinance) that says that yellow buses on this and this route can have moving stop signs?

[sokoloff]

Obviously, there is law that forms the basis for this. In Massachusetts, it's MGL c. 90 § 14

https://www.mass.gov/info-details/mass-general-laws-c90-ss-1...

[addandsubtract]

Yes, in the US, school buses come equipped with a stop sign that they extend when stopping to let kids on and off the bus. You (as a driver) are required to stop (and not pass) on both sides of the road while the bus has their sign extended.

[q3k]

It's almost as if we need human-level intelligence to be actually able to reason about the nuances of applicability of traffic signs :).