The pinecone is an occult symbol of the pineal gland in the human brain. The gland, otherwise known as the third eye, has a significance of intimate hidden spiritual importance and is very worth your future research. 

Funny how you only really see this symbol on buildings of material wealth and resource. There also just happens to be a giant Pigna statue in the courtyard of the Campus Martius area of the Vatican in Rome. Surprise surprise.