The Mutant Registration Act is similar to the one presented in X-Men. Mutants are forced to present themselves as mutants, along with their powers. In it's simplest form, it would be an addition to the usual ID of citizenship, including the mutation and such. Those that are less fortunate and have powers that are deemed "too powerful to control" would be held in custody with appropriate countermeasures and the imminent threat that they will be executed with the wrong move of a finger.

If things escalate too much, we'd have mutants running around with clear mutant identification or mutant concentration camps. Pretty much like the opening scene from Days of Future Past.