Thief grabs £10,000 diamond ring
The man walked into the shop in Skipton town centre at midday on Wednesday and asked to view items from the display.
But while the assistant's back was turned, he took the ring – worth 9,535 – and ran out of the shop.
Pc Andrew Bell, of Skipton Police, said: "This is a very distinctive ring that will stand out to any jeweller or dealer who is offered it..
"I also have a good description of the offender and appeal to anyone who saw a man in Skipton town centre wearing that noticeable jacket either before the theft or running away afterwards to get in touch with me."
The suspect is described at white, in his mid-30s, 5ft 10 to 6ft, chunky but not fat, with short dark brown hair.
He was wearing a distinctive black and white jacket with the colours merging in the middle in a zigzag pattern, blue jeans and light brown trainers.
The ring is a Hearts of Fire diamond solitaire, containing a 1.02 carat H colour Si1 clarity perfectly cut diamond carrying reference number HOF89186.