A Tobago Stamp Variety.
During the period in which Tobago issued its own stamps many stamps were overprinted to meet shortfalls in particular values. As the process was somewhat crude many varieties and errors were made.
The above stamp is one such variety; the “Long Tail Variety” listed in Stanley Gibbons Catalogue. The “tail” refers to the additional black dash seen at the tail of the large 2. This only occurred a few times on a sheet and so it is rarer than the normal type and commands a premium.