The shape is either a triangle or a diamond. Looking at our samples (we have more than shown) I would say that trian­gles as a rule stand on their own. The diamond may be a sign on its own, but is often integrated in a larger panel: a rectangle or an irregular hexagon.

Sometimes weird shapes are found reminding me of the roadsigns found in The Azores and Madeira because of the strange melting down effect and the presence of a small second heap. But it is also possible that the ministry learned from Mauritius and hired a primate to do the hard work.