The returner can signal a fair catch when returning a kickoff or punt. On a fair catch, the returner asks for a unhindered attempt at catching the kick. To signal a fair catch, the returner will hold his arm up into the air.
PRO TIP: On a fair catch, the returner is not required to catch the ball. If the returner decides not too and then touches it, it's treated as a fumble.
Fair Catch Interference