While many Americans may only be vaguely familiar with the idea of "cruising," there is a secret world of sex between men that exists in public places across the country.
The police officer who arrested Sen. Larry Craig, R-Idaho, in a men's restroom at the Minneapolis airport for allegedly looking to engage in gay sex wrote in his June report that he "recognized a signal used by persons wishing to engage in lewd conduct."
Craig tapped his foot up and down and swiped his hand underneath the bathroom stall in which the undercover cop was sitting, according to the police report.
Those actions led to Craig's arrest by Detective Dave Karsnia and the senator's guilty plea to a disorderly conduct charge. Craig told reporters today that he did nothing inappropriate and said his guilty plea was a mistake.
Public places like men's restrooms, in airports and train stations, truck stops, university libraries and parks, have long been places where gay and bisexual men, particularly those in the closet, congregate in order to meet for anonymous sex.
Over time, people familiar with cruising told ABCNEWS.com, gay men began using a codified system of signals to indicate to others that they were interested in sex. In an effort to curb lewd acts in public — or as some gays argue, in an effort to persecute gay men — undercover police began sting operations in places known for sex soliciting and employed the same codes.
"Tapping of the foot is pretty standard for men who cruise in toilets," said Keith Griffith, owner of Cruisingforsex.com, a Web site on which visitors post locations popular with men looking for anonymous sex.
"They will usually go to the stall at the far end of the strip of toilets. They will see each other and usually decide to go someplace else. The vast majority have no interest in being seen. They may be meeting in public locations, but they will be as discreet as possible," Griffith said.
Cruising areas traditionally have been those parts of town "women and children are told to avoid," but through word of mouth, bathrooms at places like Wal-Mart or Home Depot can become cruising locales, he said.
Griffith said that officers involved in such stings tend to be young and that anecdotal posts on his site indicate the local arrest rates increase around the time of elections or when media attention focuses on the issue.
Because much of the signaling is itself benign behavior, some gay rights activists and lawyers have admonished police departments for arresting men who have done little more than tap their feet.
"Citizens have a right not to confront lewd activity in public places," said Steve Sanders, a lawyer and gay rights activist. "But if there is evidence that a sting is motivated by anti-gay animus, that may represent a more troubling issue."
At trial, Sanders said, police would have to prove that actions such as foot tapping were known signals for soliciting sex.
"What constitutes probable cause to arrest someone? If a case like this went to trial, police officers would have to produce evidence to say here is how we can say with certainty this is was really a lewd act," he said.
Craig pleaded guilty to the charges and therefore opted against a trial.
Today, Craig denied being gay and said he made a mistake by pleading guilty.
Police officers, for the most part, only investigate an area after members of the public have complained about it being used for sex, said Rich Gregson, executive director of the California Peace Officers Association.
"Police officers will investigate areas that have known histories of this sort of activity. They rely on their own knowledge and experience to tell what is happening. Most officers know the difference between an intentional signal and a stray motion," he said.
The public has a right to enter public areas without worrying about inadvertently seeing lewd acts, Gregson said. The 35-year veteran police chief said he believed this sort of activity took place "in every jurisdiction" and heard stories of "off-duty officers and even judges being caught and arrested."
With many other options available for gay men to meet each other, Gershen Kaufman, a professor emeritus of psychology at Michigan State University and author of the book "Coming Out of Shame," said public cruising is practiced mainly by deeply closeted men.
"Cruisers are not sex offenders. They are deeply, deeply closeted. There is a lot of self-hatred and shame and they can't allow themselves to come to terms with their sexuality. There is also the added element of danger and being discovered," he said.