Before the trike was sold I made up a tail flasher to make it more visible from behind.
For the light I used an old LED back light that was used for a green LCD. The LCD was killed by mistake a long time ago but the green backlight still functioned fine. I attached it to the back of the battery box used for the trike lights. Its power was drawn from the same line as the front lights on the trike so the tail light came on when they did. To make it more visible I also put together a flasher circuit which was heat shrink’ed and put in with the other parts in the battery box.
The end result wasnt overly bright but it was enough to get noticed. Youtube video to give you the general idea.