The flight symbol has not been the only element added to some winglets. Some 737-800s have been spotted with a red stripe on the top of the outer side of the winglets, but it is not clear why.

Plane passenger spots unexpected and strange symbol on Ryanair flight ... These markers, which can be either red or black, are strategically placed within the cabin.

Plane passenger spots unexpected and strange symbol on Ryanair flight ... These markers, which can be either red or black, are strategically placed within the cabin.