Radiobeacons; they're either as big as a box of cigarettes or a book and will have orange markers on 'em. Should be easy to see.

[Logan hefts the black box for her to look at; aside from the color, it's a fairly standard voyage recorder, with a GPS locator bundled with it.]

Things like this one are sneakier; they're to keep the boat from getting stolen so easy. Bring whatever you find this way.