A Manhattan federal jury has confirmed something you probably knew all along: It seems throwing political protesters in the slammer, instead of writing them a ticket, kinda sorta interferes with the First Amendment. The NYPD’s lock-’em-up policy, born amid the paranoia of 2001, was short-lived (it’s already off the books) and resulted in about 30 arrests, which now may mean 30 settlements for NYPD to cough up. The biggest mistake the boys in blue apparently made was committing the policy to the books in the first place: Nothing leaves a paper trail like, well, paper. The demonstrators’ side alleged that the practice had existed for years as an unwritten rule — ever since the 1999 Amadou Diallo shooting and the spate of rallies it occasioned. Lacking concrete proof, the jury didn’t buy it; if it had, the city would be looking at about 350 more settlements. Darned First Amendment.