LYNN – Every pit bull in the city must be leashed and muzzled when it is not on its owner’s property, beginning Friday.The muzzle law, which amends the city’s vicious dog ordinance, was enacted after a rash of pit pull attacks, including one that left an infant badly mauled.A stipulation in the muzzle law allows pit bulls to go unmuzzled in public if the dog has been registered with the city’s animal control officer, is licensed by the city clerk and has passed a nationally certified behavior course specifically designed to reduce aggressiveness.City Clerk Mary Audley said officials are working out the details of how to distinguish a pit bull that has passed the behavior course from a dog that has not undergone the required training.”So far, nobody has walked in with a diploma in hand from an animal behavior class. I don’t anticipate a flurry of them coming in,” Audley said. “As it stands, the law goes into effect on Friday. The dog officer will handle the registration, which requires the owner to show a photo ID and also a photo of the dog. This office will issue the licenses.”If a pit bull owner produces a behavior-class completion certificate, it will be registered with the animal control officer, she said.The clerk’s office is creating a registration form for the pit bull owners.A Lynn dog license costs $4 for a spayed or neutered animal and $7 for those that are not.”We have purposefully left the prices low, knowing Lynn isn’t a rich city, but it hasn’t helped increase the number of registered dogs,” she said.City officials are considering a colored collar tag for pit bulls that have received behavior training and are allowed to walk the streets leashed but not muzzled.Pit bull owners must also post a sign on their property that warns “Beware of Dog” or notes that a pit bull is on the premises. Further, no single household can have more than two pit bulls.