A year after Edmonton police put up "Report A John" signs on a known prostitute stroll, officers and business owners say the program is working.

The signs ask people to report the licence numbers of vehicles driven by people who may be looking to buy sex.

"There was a lot of frustration that built up with the businesses: 'What do you do about the johns?'" said Peter Rausch, a spokesman for more than 200 businesses on 118th Avenue.

"I think most of the people believe that there has been a decrease in the amount of johns trolling in the middle of the day."

In 2006, after the program was launched in July, police received more than 800 phone calls. So far this year, they've gotten another 500.

Kate Quinn, who works with prostitutes, said some critics say the signs only attract more johns to an area, but she doesn't agree.

"So a guy now knows where to go, that's true. But the prostitution was already happening there and we see it as a stronger symbol of a community saying we don't want this activity."

After police receive a complaint they verify the facts and then send a letter to the registered owner of the vehicle, telling them that their vehicle has been spotted in an area known for prostitution and that there are health issues around prostitution.

"They've potentially got a lot to lose. I can only imagine if somebody's wife opened up the letter or their boss opened up the letter," said Staff Sgt. Bill Spinks, who heads the police program.

Spinks said police can't lay charges unless they see the crime committed, but he thinks the letters are a strong deterrent and he has never seen the same vehicle re-offend.

There are more than 500 prostitutes working in Edmonton. Quinn said there are more than 10,000 johns.