Detectives have appealed for witnesses after the theft of the £15,000 watch on Wednesday, June 16.
The victim, aged 77, was reportedly approached by a woman, who 'gave him a hug and took his watch'.
Sussex Police has released a picture of a woman, who 'may be able to assist with enquiries'.
Detective Constable Jamie Carruthers said: "We have received several reports of thefts and attempted thefts of high value watches in the West Sussex area recently.
"We believe that various individuals are responsible for these thefts.
"We are urging residents to be vigilant if approached by a stranger and urge anyone who witnesses any suspicious behaviour to come forwards."
Anyone with information is asked to report it online or call 101, quoting Operation Overdrive.
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111.