Virtual Light by William Gibson

The plot centers around Chevette Washington, a young bike messenger who, on a whim, steals a pair of dark-rimmed glasses from a man at a party because she is offended by his demeanor. Soon after, she realizes that the glasses have unlikely importance, as security company henchmen begin tracking and following her. Meanwhile, Berry Rydell, a former cop-turned private security agent, is contracted to recover the pair of glasses for Lucius Warbaby, an intimidating and presumably successful "skip-tracer", a sort of bondsman/bounty hunter.