The San Francisco Police Department is warning residents to be on the lookout for gaping holes in the sidewalk, thanks to widespread theft of utility covers.

Be careful while walking in San Francisco. That’s the message police issued Thursday as they try to track down who’s responsible for stealing sidewalk utility covers around the city.

San Francisco police are asking the public to report stolen or missing utility covers on sidewalks that are creating hazards for pedestrians. The San Francisco Public Utilities Commission has reported more than 400 stolen sidewalk covers in the last two years,