Here is a Coventry Electric Tramway cover from 1904 with their 2d parcel label used as a railway fee stamp.
From Wiki: "On 6 March 1900 a tramway postal service was inaugurated, which continued until the end of tramway operation 40 years later. In latter days the postal car left Bedworth at 8.50pm, showing 'Postal Car' in red letters on the route indicator. The letter-box was fixed to the outside of the rear dash."
