Maine Revised Statutes (MRS Title 29-A section 1251) require you to be licensed if you are going to operate a vehicle. Here it states that a person commits an offense of operating a motor vehicle without a license if that person operates a motor vehicle on a public way or parking area. Subsection A notes that driving without being licensed is a violation of this paragraph and is a Class E crime, which is a strict liability crime.
In Maine, a Class E can allow you to be arrested and go before a district court judge. A Class E crime carries a penalty of up to $1,000 fine and up to six months in jail.
Operating without a license is also a traffic infraction worth 4 points on your ME driving record. The Maine Bureau of Motor Vehicles (BMV) states that the license, permit or privilege to operate of any person convicted certain offenses may be suspended for a period up to 30 days. In the list of offenses is operating a motor vehicle without a license (crime).
If you were cited for being an unlicensed driver you can contact the court listed on the ticket for more information about your possible penalties and/or contact the ME BMV.