Triangular road signs are available in 450mm, 600mm and 750mm sizes.
Class RA1 Engineering Grade or RA2 High Intensity Prismatic reflectivity
Wall mounted or with rear channel for post fixing
DOT Transport Diagram 544.1
In areas of street lighting (except on motorways), a speed limit of 30mph applies unless another speed limit is specifically signed.
Both the give way and stop sign are regulatory signs, meaning that they are giving an order.
The difference between give way and stop sign other than the shape, is the text telling you what must be done. A give way sign tells you that you must give way to traffic ahead and a stop sign tells you that you must stop.
Official specification Sign Posts.