The gov.uk website still shows a common signage for England, Scotland and Wales.
So long as the sign is still round, with a white background and a red border, for law enforcement purposes it is surely irrelevant what the number displayed on it is and the statement that it makes obvious, even to the uninitiated. I presume that a speed limit sign has to be of a certain size and the mph limit displayed on it has to be in a certain font, but that it would comply with requirements regardless of what mph value is actually shown, so its not really something that is specific to Scotland.