By setting an SLR camera to "Shutter Priority", you can then control the amount of time the lens stays open. Here I set the shutter speed to about 5 seconds and used my phone to write my name in the air. Because the lens was open, it took in the light of my phone.
If you are going to try this:
1) Find a dark room.
2) Put your SLR camera on a tripod and set it to shutter priority (the "S" setting on most Nikons).
3) Set the shutter speed according to how long your name is (try and use a short nickname).
4) Have someone press the shutter button and you will hear the shutter sound then start.
5) Write non symmetrical letters backwards, (B, C, D, E, F, G, J, K, L, P, Q, R, S, Z).
6) Start from right to left and use all capitals (go slow or you will have really faded letters).
7) If you name is being cut off by the camera, move it back and crop out excess stuff later.