The only hint of their presence in Midtown’s Hotel Pennsylvania—the lobby still garlanded for the holiday season and crowded with milling tourists—was a 20-something guy shuffling around in medium-rinse jeans and a lackluster black leather jacket. He might have been one of the tourists himself were it not for the fluorescent pastel sign he held reading: THIS WAY TO BRONYCON! Pictured on the sign was a pink and purple pony in a green field.

The so-called Bronies—a herd of mostly male, mostly white, mostly mid-20s fans of the animated TV show "My Little Pony: Friendship Is Magic"—have had plenty of press coverage of late, but this [...]