We have adaptive brake lighting upon harder stops than normal. I think I read when the braking force is enough for a briefcase to slide off the seat onto the floor, enough braking force is used which turn on extra lamps out back.

Anyways I made a video a long time ago when youtube wasn't around but luckily someone copied it and put it up on youtube. :D

http://www.youtube.com/watch?v=h35smNCI6lY

Now I am wondering what I could do to tap into that light so when full power to the light comes on, it trips a circuit to open/close to make the light flash instead of just turn on. Flashing would get someone's attention...an extra brake light would mean nothing to the average driver until they see the trunk contents.