Theoretically there is a license required, but 99.9% of the contractors do not have one. You will need to actually petition the Registrar of Contractors to get a license classification. They will probably put you in an L-5 graffiti removal and abatement classification.
That being said, it probably would not be worth it to you as you start out. As you go and give proposals for larger jobs you might want to look into a license.