The stamp on the left is SG 40 but I can't find the stamp on the right in the SG Commonwealth catalogue.
The problem is the imprint that differ from each other.
Maybe there's another catalog that contains him...
Interestingly enough, Smithsonian magazine ran an article in their last issue describing the island of St. Helena as Napoleon's place of exile, after Waterloo, and where he died. VERY interesting and informative!