Which of the following is a common sign of otitis media?

A bulging tympanic membrane is a common sign of otitis media, which is the inflammation or infection of the middle ear. This condition often results in the accumulation of fluid behind the eardrum, causing it to bulge outward. The bulging occurs due to increased pressure from the fluid build-up as the eustachian tube becomes blocked. Physicians typically assess the tympanic membrane during an examination; a bulging appearance suggests the presence of infection or inflammation.

The other options reflect findings that would not be indicative of otitis media. A normal tympanic membrane would suggest that there is no infection or inflammation present, while a clear ear canal, free from any discharge or blockage, typically indicates health rather than a potential infection. Similarly, a lack of redness in the eardrum would also imply that there is no inflammatory process occurring. Therefore, the presence of a bulging tympanic membrane is the key sign that points to the diagnosis of otitis media.