What can fans do to stand out at the concert?

One or two flashlights per person should be fine. The flashlight sweeps back and forth on your banner, which not only illuminates the banner, but also has a considerable number of apertures.

Cleaning actions can be arranged, with regular collective movements and irregular cleaning intersections.

The banner should be big and the flashlight should be bright.

I think it will have some effect. (only by personal imagination, not practiced. )