How can you find out what a World War 2 military pin symbolizes?
Are there any words on the pin? It is probably a distinctive unit insignia.
Here is a link to some simple explanation for the brass worn on the uniform.
If you refer to the Distinguished Unit Insignia(DUI or DI) pins, then there were hundreds of variations on these and you need a reference book for this. Here are samples for a few units that fought in Italy.