There was a time, about a century ago, when prostitution was perfectly legal in Dallas at least so long as it took place in Frogtown, the city's official red-light district. It was a decidedly pragmatic way of dealing with the world's oldest profession, but it wouldn't last. The state's Supreme Court shut it down after a few years, and the city, like pretty much everywhere else, gradually adopted a more punitive approach to the sex trade.

The pendulum now seems to be swinging back away from punishment, with Dallas County's pioneering prostitution diversion initiative attempting to funnel women into treatment rather than jail. The program is now primed to go statewide.

The program's goals and outcomes are laudable, but its success is built on a constitutionally ambiguous premise.

See also - Guilty Look: In Dallas, Chatting on a Street Corner Can Get You in Trouble - Dallas Cops Showcased a Treatment-Centered Approach to Prostitution Last Night, Which They Hope Can Be a Model for the Nation

Before they enroll in the program, women have to be arrested first, which typically happens during monthly sweeps of truck stops along the Interstate 20 corridor. No problem there. Some of the women are taken into custody after soliciting undercover vice cops. No problem there, either. When you take money from a cop in exchange for sex, he has plenty of probable cause.

The majority of the women, though, aren't actually caught performing sex acts for money, nor are they caught offering to do so. Most are arrested on a charge of "manifesting for the purpose of prostitution," which is where things get weird.

Take the alleged prostitute and john who were arrested early Wednesday morning. A couple of beat cops (not part of the prostitution-diversion efforts) were on patrol in South Dallas at about 1 a.m. when they spotted the woman walk up to the man in the Chevy pickup that had stopped near the intersection of Malcolm X Boulevard and Hatcher Street.

Nothing happened, according to a police report. The woman stood by the man's window and they talked until she spotted the cops and walked away. But the officers suspected the woman of being a prostitute and interviewed the man and woman separately. She said she'd just been giving the man directions. He said he'd just given her a ride from a nearby store.

The police bought neither story and ticketed both for, as the police report puts it, being "engaged in conversation in high-prostitution area."

That seems like an incredibly flimsy reason for a criminal charge, but it's been on the books since the 1970s. Beckoning to people and trying to stop passersby also qualify as crimes under the city's manifestation ordinance. No sex or exchange of money necessary.

It's not entirely clear whether the provision adheres to the constitutional ban on unreasonable search and seizure, which requires police to have probable cause before placing someone under arrest. A lengthy piece that appeared in Salon in 2010 suggests that defendants tend to prevail in such cases but only if they challenge their citations in court, something they rarely do.

And the Observer ran a piece back in 2004 questioning the legality of Dallas' ordinance. (There's one for drug dealing, too.) A city prosecutor defended it by saying it helps fight crime and has never been found unconstitutional. "And they've certainly been there awaiting any sort of challenge."

It's undoubtedly a good thing that police and prosecutors are using these citations as leverage to guide women off the streets rather than merely as punishment. But is it a good thing that someone can be picked up on a prostitution charge for talking to someone in a high-prostitution area? Hard to say.