What are the symptoms of a bent derailleur hanger and how can it be identified and fixed?

Symptoms of a bent derailleur hanger include difficulty shifting gears smoothly, chain skipping, and noisy operation. To identify a bent derailleur hanger, visually inspect it for any signs of misalignment or damage. To fix it, a bike mechanic can use a derailleur hanger alignment tool to straighten it back into proper position.