Any sign posted that indicates that firearms are not allowed is valid. It will allow the property owner to file criminal trespass charges against anyone who carries, open or concealed. My understanding is that open carry is legal in Louisiana, but you will probably be questioned by LEO's. You can't carry anywhere that serves alcohol and does not allow access to minors. They do not allow carrying during parades, public gatherings, at places of worship, or hospitals. The biggest difference is the fact that any kind of sign is valid.
Cajuns are friendly folks, what kind of business takes you to Louisiana?
I travel there on a fairly regular basis, I always carry. I do suggest staying at the newer hotels. During the week, you can sometimes get a nicer room at the casino's hotel for less than you pay at regular hotels.