Captain J.J. van der Starre was given in Watercraft Philately 1980 page 80 the following on this stamp.
On 15 September 1979 Brazil issued a definitive stamp of 3.30 cr depicting a boat and boatman of the San Francisco River.
Said to be used as a kind of ferry, the craft has a striking figure-head resembling an animal. The head is well-worked and indispensable in the traditional craft of the Brazilian river in this strange form and is, to the crew, their total security. One of the tales of superstition says that the weird figure lets out three growls before its inevitable sinking.
Brazil 1979 3.20cr sg?, scott1655.