The important role played by African members of the French Resistance has long been neglected, but it is important to note that some of the first to support the movement were overseas territories in North Africa.
In 1944, French Equatorial Africa overprinted some of its 1941 issues to produce a semi-postal set for which the excess non-postal funds were used to support the French Resistance (Scott #B12-21). Only 10,000 sets were issued, and Scott '14 prices the unused set at $198.00.
The set strongly appeals to French Colonies collectors, as well as World War II topicalists. Furthermore, since the former colony of French Equatorial Africa was granted independence and divided to form the current nations of Chad, Congo, Gabon, and Central African Republic, the set makes an interesting emerging market play as well.
Those interested in learning about investing in stamps should read the Guide to Philatelic Investing ($5), available on Kindle and easily accessible from any computer.