Local school put up those sign all over the street – are those city signs and are they enforceable?

I just noticed the local school put a dozen of those all over the street in our residential neighborhood. They are telling the whole neighborhood not to park on the whole street (over a 500 ft stretch). Theres no days or hours, just a blanket “no parking”. People living on the street have been relying on those parking spots for years. Are those signs from the city? If not, are they really enforceable? Can a school just decide they want to reserve themselves two full block worth of street parking (at the expense of the locals that live on the street)? Thanks!