Attire?

My fiancé is in the Navy, and his LPO recently got promoted to chief. We were really close with their family for the 2 years that we've been here, and they invited us to his pinning ceremony tonight. I asked my fiancé what the attire would be, and he told me to wear "anything", which I'm sure means there is some kind of dress code that he just doesn't know about, or maybe it actually is casual...

Anyways, we're not participating in the ceremony or anything, but is there a dress code for this? I was thinking jeans and a nice shirt- mainly because we are just attending the ceremony.