A gold pocket watch given as a gift by former US president Woodrow Wilson was stolen from a UK antiques shop.
The 14-carat timepiece worth £15,000-£20,000 ($20,000-$26,677) was snatched by a man pretending to be a shopper.
The thief entered the shop in Islington, north London, and said he was interested in buying a vase, London's Metropolitan police said.
In the confusion caused while his card payment was declined, the man opened the display case and ran off with the watch at 12.30pm on Saturday.
The watch was given as a present to the current owners by Woodrow Wilson – the exact circumstances were not made public.
Mr Wilson was the 28th president of the United States and served from 1913 to 1921.
He was born in Virginia and led the US into World War 1. He was also the first southerner to be elected president since the country's civil war.
"The owners of this watch are very distressed. The item had been in their family for a long time and I would urge the person who stole it to return it as soon as possible," said PC Joshua Brown.
Officers released images of the watch, as well as a CCTV image of the person to whom they want to speak.
