Your hero has committed some crime and will be arrested if discovered by the authorities. This assumes the setting actually has laws and police officers to enforce them.
The level of the Hindrance depends on how serious the crime was and how active the hunters are. A hero with numerous unpaid parking tickets (in a game where he might have to drive occasionally) has a Minor Hindrance, as does someone wanted for more serious crimes away from the main campaign area. Being accused of murder is a Major Hindrance in almost any setting if there’s someone around to seek justice (or vengeance).