Certainly the easiest is a re-brand. In fact, I'd approach Square with "we're willing to fight this, and it's going to cost both of us a lot of money...but with a proper financial incentive from Square to cover the costs associated with re-branding, we might be willing to entertain that option" (written in lawyer-speak, of course). An acquaintances company was basically paid mid six figures to change their name in somewhat similar circumstances, and they used it as a opportunity to do some interesting things, marketing wise.