I can only talk about the Netherlands:
Round white sign with a red band, black letters: maximum speed
Square blue sign with white letters, advisory speed (advisory speed < maximum speed - 20 )
There is no minimum speed (round blue sign white letters): this is for the simple reason you could technically be ticketed in the case of a traffic jam, yield sign or traffic light
I can only talk about the Netherlands: Round white sign with a red band, black letters: maximum speed Square blue sign with white letters, advisory speed (advisory speed < maximum speed - 20 )
There is no minimum speed (round blue sign white letters): this is for the simple reason you could technically be ticketed in the case of a traffic jam, yield sign or traffic light