You are walking around LSU campus after the Aggies crush the Tigers in their SEC match. You find an unusual tree with fan-shaped leaves. The presence of which would immediately prove that this tree is, in fact, a Gymnosperm?

exposed ovules

Explanation:

Gymnosperms are a type of flowerless plant that tend to produce cones and seeds. This is why the name refers to "naked seed", seeing since the gymnosperm seeds are not positioned within an ovary. Therefore the presence of exposed ovules or the structure that contains the seeds in a place would immediately indicate that this is, in fact, a gymnosperm.