[Colin Heichman]

Well, I’m still learning Motion so I might be wrong.

But it seems as if this effect would be created in two layers. It’s kind of a magic trick. You put the logo out there but transparent. Then you put something over it and when that “something” is gone, it’s no longer transparent.

The top layer would be the light streak, created with a “sliding window” of write on behaviors.

Underneath, there is a layer with the “C” graphic to be left behind.

Start the animation with the opacity of the “C” graphic set to zero.

Tweak the light streak so that the beginning and end of the streak cover both ends of the logo at some point in the animation.

Keyframe the opacity to zero on the frame before that point and 100% on the exact frame where the logo is covered. As the light streak “writes off”, it’ll reveal the logo which was there all the time but transparent.