Each year, when Southwest achieves the #1 position in certain DOT standings (I think in something like on-time performance, baggage handling, and passenger satisfaction, but correct me if I'm wrong), they award themselves with a "heart", which is part of the whole "LUV" theme. After winning in these categories three years in a row, they called it the "Triple Crown" and painted an aircraft accordingly. I don't think they actually achieved what they call the Triple Crown, however, because the year they painted that aircraft, AWA won #1 in baggage handling.
I find it odd that few people in the general public (including myself) really know what it means.
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Photo © Michael F. McLaughlin