Hi thanks for writing in! Usually you see a 18 "KT" or "CT" to designate the gold purity but then again there are so many exceptions, and surprises, the plus sign could even mean it's more parts per gold than 18 carat gold. Most quality jewelry is made of 18 kt gold and higher.
If you don't have access to digital gold testing equipment, your local jewelry can acid test it for you, it shouldn't cost very much for this simple test. The color of the metal of the pin, has a pink caste, it could also be rose gold. Have it tested.
