A Norfolk post office was robbed by two men who were believed to be armed with a gun.
The two men escaped with the takings from the post office at Upwell, near the Cambridgeshire border, after robbing the store at about 1720 GMT on Tuesday.
Norfolk Police said they were keen to hear from anyone who saw the men as they were likely to have been covered in a dye which had been concealed in the money.
The security dye would have been activated when the robbers left the post office and may have leaked onto their clothes and skin.
Officers would also like to hear from anyone who saw a burgundy Vauxhall Cavalier being abandoned in village shortly after the robbery.