That's right, zooming on long exposure. 2secs in this case. I think I tried zooming in as well as out about 5 times each way. The effect is different for in and out.
This shot was done on a small clamp on the railing. A sturdier support would have helped a lot. You can see that the lines are not perfectly straight due to slight jerking during the zoom action.
Probably a nicer effect could have been achieved if a recognisable symbol were located at the centre.