I don't think you're right. I'm not a CPA, but work in a related industry. I've never been in situation where I've received a signing bonus, so I don't have personal experience. I do recall, however, that if a signing bonus is not related to playing in actual games, it may not work that way. I know that typically cash is taxed, but it may not be the case, especially for the employer. Federal and State taxes could be treated differently. Plus, I would think a signing bonus has nothing to do where you play your games. It's where you live. Guess what? A lot of these players have their residence in Florida. Hmmmmm.
In other words, I don't think MN gets jack on a lot of signing bonuses.
I'll wait to hear from someone who has a working knowledge of this.