It sounds like leaf miner damage. They tunnel/feed between the front and back surfaces of the leaf until eventually they come out to drop in the soil below and pupate. I've never had them on tomatoes before, but I do get them on Aquilegias. I usually consider the "scribbles" a good sign -- they're STILL in there. Just snip off the affected leaves (If the plant is small, I sometimes use scissors to just cut out the scribble
) and dispose them -- not in compost.
I guess this advice doesn't work so well if you have a LOT of affected tomatoes. I'm beginning to understand the huge range in the scale of gardens folks have around here.