Claim: NGC 5866 is an asterism and not a constellation.
Evidence: NGC 5866 (also called the Spindle Galaxy or Messier 102) is a relatively bright lenticular or spiral galaxy in the constellation Draco. One of the most outstanding features of NGC 5866 is the extended dust disk, which is seen almost exactly edge-on. It is also possible that the galaxy is a spiral galaxy that was misclassified as a lenticular galaxy because of its edge-on orientation, in which case the dust lane would not be too unusual. Draco S0 ~60,000 ly
(18,400 pc) 4′.7 x 1′.9 The galaxy is viewed edge on 
In observational astronomy, an asterism is a popularly-known pattern or group of stars that can be seen in the night sky. This colloquial definition makes it appear quite similar to a constellation, but they differ in that: a constellation is a formally-named area of the sky and all the celestial objects within it, representing an object, person, or animal, often mythological; while an asterism is a visually obvious collection of stars and the lines used to mentally connect them. As such, asterisms do not have officially determined boundaries and are therefore a more general concept which may refer to any identified pattern of stars. This distinction between terms remains somewhat inconsistent, varying among published sources. An asterism may be understood as an informal group of stars within the area of an official or defunct former constellation, or crossing the boundaries of two or more constellations. 
A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived outline or pattern, typically representing an animal, mythological person or creature, or an inanimate object. A more modern astronomical sense of the term "constellation" denotes one of the 88 IAU designated constellations recognized today.