Presumably, if it says Palestine, you should deduce that it is Pre-1948. But that doesnt take into account the time it may have taken for artisans to make new stamps. I think it likely that it is from the 40's, but it's just my guess.
Definitely pre-1948; the trouble with many Eastern (from Levant onward) items is that a design might be made for decades or longer - carpets, porcelain, silver - with more concern over the perfection of the object as opposed to the introduction of new elements. A rather basic difference in thinking from that of the West. So one has to look at the actual metal. Please post a picture of the back of the brooch.