BattleMech Manual (p. 83)
A íMech with the Distracting quirk is physically designed to intimidate (or confuse) its opponent with its appearance. This includes the fearsome visage of the Atlas
BattleMech, but can also include íMechs cosmetically designed to appear more heavily armed or deadly than they truly are, such as the Arbiter
A íMech with the Distracting quirk applies a +1 Special Source modifier to any Morale Checks its opponents must make when using the Tactical Morale rules. If using the Demoralizer Special Piloting Ability from Campaign Operations, the Distracting quirk adds a +1 modifier to the demoralizerís WIL score.
This quirk may apply to a íMech in some periods but not others: for example, the Mackie
would almost certainly be Distracting upon its debut, but would lose the quirk once the novelty wore off and newer designs were introduced.