Tetrahedron

from Fancyclopedia 2 ca. 1959

A triangular pyramid. In position of two such-shaped spaceships set for ramming, a pair of tetrahedra bracketing a publication's title indicate that it's from Speer's publishing house (below).

from Fancyclopedia 1 ca. 1944

A solid bounded by four planes, the smallest number that can enclose a solid; a triangular pyramid. In positions of two such-shaped spaceships set for ramming, a pair of tetrahedrons around a publication's title indicates that it comes from Speer's publishing house.