PHILADELPHIA (WPVI) -- Philadelphia police are on high alert after reports of threats to some of the city's finest.Three Philadelphia police districts were named specific targets for terrorists: the 2nd district in Northeast Philadelphia which also houses the Northeast Detective division, the 6th district on the edge of Chinatown, and the 35th at Broad and Champlost in Olney.The tip was passed to a patrol officer by a woman who flagged him down on the street.Detectives have investigated the claim, but no credible threat has been uncovered."We take all those threats seriously. We investigate them. Right now, we haven't found anything substantive, but we are going to take each and every one of them serious, as we do with threats against the public," Philadelphia Police Commissioner Richard Ross said.Some police sources say these kinds of threats which are relatively frequent have increased a great deal since last week's deadly attack on Dallas police.With the Democratic National Convention coming to the Wells Fargo Center later this month, police are gearing up for mass protest demonstrations and potential terrorist strikes.With those challenges straight ahead, it's a very busy time for at the headquarters of the Delaware Valley Intelligence Center, an agency which monitors, collects, and analyzes data, video, and social media from southeastern Pennsylvania, southern New Jersey, northern Delaware, and down into Maryland."We got the DNC coming up so we have to be very much aware of all these things. The bottom line is we don't do this alone either," Ross said.