The stamp "BREV" on gold stands for "Brevetto." This is the Italian term for license, and the stamp signifies that the particular design or piece has been licensed or patented.
The inscription is often followed by a set of numbers that can be used to further identify the original creator or licensee. BREV refers only to the ownership of the design, not to the gold content or purity, and the inscription can be seen inside jewelry, music pieces, pipes and a variety of other gold items. There is a similar patent inscription "Brevet," which refers to a French patent, but this inscription is spelled completely out, whereas the Brevetto inscription is most often abbreviated to BREV.