While rap began in the underground, the genre's evolution and gradual mainstream acceptance opened the door for artists who were brazenly anti-commercial and/or proudly independent, indifferent to the exposure promised by major-label promotion and distribution. Underground Rap has no sonic signifiers. It can be raw and unvarnished (hardcore lyrics over stripped-down beats), left-of-center to an extent that it has no potential to cross over, or emulate mainstream rap production on a low budget. It is an umbrella term that groups weirdoes like Ultramagnetic MC's, firebrands like Paris and the Coup, and gangsta rap entrepreneurs who sell mixtapes out of the trunks of their cars.