So I contacted the City Attorney who directed me to contact the District Attorney's office. While talking to an Assistant City Attorney, he told me open carry was illegal. I asked him what statute it violated. He said, I don't know, but we arrest people for it all the time. Then he told me if I Googled it, I could probably find it.
I called the DA's office, left a message, no return call. I called OSBI for a different reason and ended up talking to someone in their legal department who told me it would be up to each DA's office on how broad or narrow they interpreted "any other legitimate purpose".