BOOK SIGNING: Artist and author Justin Bua, known for his bestselling collection of fine-art posters, will be at the Booksmith tonight, along with DJ QBert, celebrating the release of The Legends of Hip Hop, featuring portraits of 50 of the greatest names in hip hop history, along with a personal essay that details each individual's impact on cultural history and Bua’s own life and work. (6:30 p.m., The Booksmith, 1644 Haight Street)

PARTY: FunCheapSF has info on the 4th Annual SF Bike Expo's Pre-Party, featuring free beer and pizza (get ready to stand in line!), along with a chance to meet and mingle with a handful of international riders like Andrew Taylor, Greg Watts, Cameron McCaul and Tyler McCaul, which is sure to get you "geared" up for the big expo this weekend. (6 p.m., Marin Factory Store, 1090 Folsom Street)

ART: Southern Exposure presents Working Conditions, a group exhibition that literally explores how artists work -- each artist created his or her own work environment as an installation within the gallery and kept regular work hours there, "while developing a project rooted in notions of production, labor, and process." (7 to 9 p.m., Southern Exposure, 3030 20th Street)