You're running a private security company, you're offering self defense advice -- yet it seems you don't understand the basics of the laws governing the use of force -- let alone a police investigation. You seem to have conflated a civil proceeding and a criminal proceeding, among other things.Hello PDG! Nice to meet you. While we don't register our hands and feet with the police, just as we have to register a gun. A MA practitioner that has registered in a local dojo, should he get involved in a fight and do some damage, he will be investigated by the police and in said investigation they are likely to find out that he is an MA practitioner because of the dojo's roaster. Should that happen and depending on the level of damage as you suggested he may be charged heavier had he never practiced. It is no secret that MA are designed for combat so a court of law may take it as if you had some sort of advantage over the other guy. Law enforcers and military personnel are prosecuted in a similar fashion since them and MA practitioners have an expertise in combat.
In brief, self defense is an affirmative defense in court. You're admitting you did something that would be wrong -- namely, an assault and battery -- but that you had a reason that justified your action or excused you from criminal liability. In the case of the use of force, you're saying that you had to harm someone so that you would not be harmed yourself, and you'll argue that your force was reasonable and appropriate to the threat presented. A toddler grabbing your neck doesn't justify lethal force -- but an 18 year old kid, pissed off, with a broken chair leg? Hell, yeah. There's a lot more to it than this, and I'm not going into at length here (it's covered in depth in several threads...) but you are generally justified in using the force reasonably necessary to safely resolve a bad situation. The only thing different for a cop versus an ordinary citizen is that, in the course of their duties, police are often permitted to use force proactively and earlier than an ordinary citizen -- but they have to be able to articulate or explain what led them to using force.
(By the way -- you don't have to register guns in every state...)