Cutie marks

The My Little Pony franchise is famous for the symbolic cutie marks, unique tattoo-like features located on the ponies' flank or haunch. In Friendship is Magic, these marks are obtained by ponies when they discover a unique characteristic which sets themselves apart from others. Once this happens, the mark appears on the pony's haunches.

Some ponies have yet to gain their mark, like Apple Bloom, Scootaloo, and Sweetie Belle. They are derisively called "blank flanks" in Call of the Cutie by other young ponies, while Twilight and other adults consider ponies without a cutie mark to be full of potential. Twilight explains to Apple Bloom that magic can't make a cutie mark appear, and that the mark will appear in due course.

Occasionally, an adult pony can be spotted without a cutie mark, which has been explained by Lauren Faust as oversights due to time constraits. Faust has also referred to cutie marks as "butt symbols" in her deviantArt comments section.

Trivia

 * The term "cutie mark" is a play on "beauty mark," a term for a prominent facial mole. Such moles have sometimes been considered an attractive feature.