The acronym "SIS" stands for "suspended imposition of sentence" and is usually accompanied by some form of probation as punishment when you are found guilty of a crime. By placing you on an SIS and ordering probation, the judge gives you the opportunity to avoid being sentenced altogether by successfully completing that probation term.
You can represent yourself on your expungement case. But you shouldn't. If you're considering getting your record expunged but don't think you need a lawyer to do it, this article is for you. Not only will an expungement lawyer make the process faster and less stressful, they will make sure it's done right so that you have the best chance of having your expungement granted.