EVERYONE knows Harley owners are serious about their motorcycles, but try to steal their prized possessions and you will realise just how serious they can be. Harley-Davidson headquarters in the United States has decided that enough is enough when it comes to the high theft rate of Harleys around the world and have signed up a detective to travel the world and track them down. Hong Kong has become something of a Harley haven in the past few years and the numbers have jumped from a handful to at least 200 pure American grunt machines plying the packed streets. But with the growth in Harley ownership and a ready black market in China, theft has also become a Harley owner's worst fear. Harley-Davidson general manager in Hong Kong, Hector Lui Wai-kuen, said vehicle identification numbers, which were like ''fingerprints'', went a long way towards identifying stolen motorcycles, but security was without doubt a major concern for Harley owners. ''We have been in communication with the police department here and now we hear that the Harley-Davidson head office in Milwaukee has assigned a full-time policeman to travel around looking for stolen bikes and to work towards prevention.'' Mr Lui said he was keen to have the detective appointed by Harley-Davidson management visit the territory for a briefing on the situation. ''There have only been about four Harleys stolen and not recovered but these are the machines of a lifetime and many people can't afford comprehensive insurance,'' he said. Harley Owners Group president Peter Gidlow said the only real security was, ''a big chain, a cover to disguise that it's a Harley . . . or buy a Honda.'' He said China was known to offer a market for Harleys stolen in the territory. ''There are people over there who will pay anything to get their hands on a Harley,'' Mr Gidlow said. A Harley-Davidson in Hong Kong sells for about $180,000 but in China Mr Gidlow said price would be no object on the black market. He welcomed the move to assign a police officer to the task of stopping Harley theft. He added that he hoped the officer could open dialogue with Chinese authorities. who at present turned a blind eye to the problem he feared could get worse.