Like the sign on an eight-year-old’s tree house, the message on hip-hop’s doormat is “Girls Keep Out.” From casual sexism to outright misogyny, the genre has historically marginalized women in general and black women in particular. Yet in the face of all that, the ladies — from pioneers like Sha Rock to game changers like Salt-N-Pepa to current innovators like Nicki Minaj and Missy Elliott — have persevered, making a mark on the music while promoting a black-feminist consciousness. That struggle has become the topic of scholarly papers, college courses, and even a feature in Ms. Magazine. Now the Rock Hall is tackling the topic in tonight’s installation of Rock and Roll Night School — Women Who Rock. As part of the Rock Hall’s annual Black History Month celebration, education staffers Stephanie Heriger and John Goerhke will lead you through the complicated roles of women in hip-hop — complete with music, video clips, and a group discussion. Class is in session from 7 to 8:30 p.m. in the Foster Theater, where seats are on a first-come, first-serve basis. It’s free. Check out the website for details.