At around 12:55pm on Tuesday, 19 April, a man stopped outside Barry Papworth Jewellers on St Thomas Street, on a bicycle.
He used a mallet to strike a glass panel in an attempt to access the items on display, but when it did not break he cycled off on his mountain bike in the direction of Stanford Hill, empty handed.
Hampshire Police said it wants to speak to a man described as white, aged 25 to 35, wearing a dark coloured hooded top and light coloured gloves. He was riding a black full-suspension mountain bike.
PC David Barnes, said: “I’d like to speak to anyone who witnessed the incident or anyone who has any information about who may be responsible. If you have any information that may help us, please get in touch and speak to us in confidence.”