THE next time you leave a fortune in jewellery lying around in a public place, you can rest assured there is a 50 per cent chance of getting it back. After a taxi driver made headlines last week by returning $300,000 in cash to a passenger who had left it in the cab, the Sunday Morning Post decided to test the honesty of Hongkong people. About $1,000 in fake rhinestone jewellery was packed into leather jewellery boxes along with invoices made out for up to $55,000 each - with a name and telephone number - and left lying around Central and on public transport. Within an hour, four out of eight boxes had been returned. Rewards for honesty should be handed to: Joyce at the Galleria, St John's Cathedral, staff of the Mandarin Oriental hotel and the attendant in the women's washroom at the Hongkong Hilton. And what had the Sunday Morning Post lost at the time of publication? One jewellery box had been left under a counter at the Hongkong and Shanghai Bank headquarters in Central, another in the back of a taxi from Central to Quarry Bay, one on a Chai Wan-bound MTR and the last one in a public telephone booth outside Prince'sBuilding. Within seconds of a ''gold and diamond'' necklace and earring set being left in the telephone booth, a Chinese man, after peering into the box, tucked it under his arm and ran off with it. And the box left on the MTR was surreptitiously removed while we watched. But there were times when it was not easy to ''lose'' the jewellery. A box left on a table at McDonald's on Queen's Road was returned to the manager by a woman with three children - even after she saw what was inside. A salesgirl at the Mondi boutique in The Landmark caught us just as we were leaving, as did a guest at the Mandarin coffee shop. Those who found the jewellery and were honest enough to return it did not doubt its value: ''Do you realise you left something very expensive behind?'' said an employee of Joyce at the Galleria, after she found the box on a chair in the middle of the store. ''You are very lucky we found this,'' said staff at the Mandarin. An employee in the office of St John's Cathedral - where a box had been left in one of the back pews - sounded highly unimpressed with our carelessness, while the security official at the Hilton hotel suggested we write a thank-you letter to the washroomattendant. The rest of the junk jewellery, it appears, will probably never be seen again. According to Maggie So, of the MTR, about 5,000 items were found in the past six months. ''Most of these items were handed in by passengers, but the rest is discovered by our staff. Most of the items are wallets and key chains.'' A spokesman for the Ten Major New Territories Taxi Trade Unions Committee, Hui Koon-wah, said: ''Usually taxi drivers report the lost property to the police or to one of the taxi associations. Money generally goes to the police station.'' And to those who decided to keep the lost baubles: Sorry, but if you try to sell them, you are in for a surprise.