Well that is an interesting pin! A real grasshopper in a cage pin! The marks on the cage could be the marks of a studio jeweller, perhaps not registered marks even. You mention it is also marked with the two digits - "18" this could be the gold standard, it could be 18 carat gold, the gold coloured cage that is. The only way to tell is to test the metal.
If you have digital gold testing equipment you can test the gold yourself. Or else your local jewellery can acid test for you. Make sure you don't get any nitric acid on the specimen, which may be rare, considering someone thought enough of it to have it caged in a jewellery type of presumably gold surround.
