What is an example of a descriptive mark?

In 2005, the Trademark Trial and Appeal Board affirmed a finding by the PTO that the mark ASPIRINA, used in connection with analgesics, is merely descriptive. Not only is the term the Spanish word for “aspirin,” but it is close in sound and appearance to the term “aspirin,” and “aspirin” is certainly a descriptive term of analgesics.

For what its worth, some question this opinion, at least insofar as it contends that consumers would perceive the mark in a specific way despite arguably inconclusive evidence.