Graffiti is an inescapable facet of urban life that can be annoying or inspiring. In the 1970s, New York City’s graffiti-covered subway cars seemed to signify a great city’s descent into blighted decrepitude, but that same milieu launched the careers of epochal artists such as Keith Haring and Jean-Michel Basquiat, and graffiti was considered a visual equivalent of hip-hop and punk music. Today Haring and Basquiat are dead, and glitz has replaced grime in Manhattan, even as graffiti lives on around the world as a democratizing force that sometimes lives up to its potential. Locally, Brandan Odums’ vast aerosol spectacles covering blighted housing complexes and huge warehouses are compelling evocations of black history painted with a narrative sense that borders on the biblical. But most graffiti here as elsewhere is more enigmatic, like so many aggressively cryptic squiggles glimpsed briefly in passing. This Top Mob show is a mostly local mash-up that amounts to an art historical survey of graffiti taggers dating back to the 1980s. Perhaps fittingly, it is exhibited in the Ogden Museum of Southern Art’s tunnel-like ground level annex, lending it an “underground” aura as physical as it is metaphorical. Here large numbers of small documentary photographs mingle with a series of street-art paintings in elaborate baroque frames, including some by familiar names such as Lionel Milton, a conjurer of stylized back-street romanticism who was originally known for lyrically edgy graffiti signed “Elleone.” Some have reacted to the befuddling complexity of 21st-century life by becoming agents of one-word branding. HARSH is both this local artist’s message and his signature, while “READ” appeared out of nowhere in 2006 with monosyllabic exhortations that have turned up everywhere ever since. Works that elaborate the idiom’s painterly potential include Go Fast, a pop aerosol expressionist canvas by Atlanta’s Dr. Dax, and King Cake and Sex (pictured), Los Angeles maestro Kelly “RISK” Graval‘s lush aerosol evocation of local sensuality.