This cool design was "tattooed" on this leaf.

I found it on the windshield of my car.

What's up with it?

That is the work of a leaf miner. A leaf miner is the larval stage of an insect that feeds on the inside layer of leaves. Notice how the galleries (tunnels) start small and then get larger as the larva matures? Most leaf miners are moth larvae (Lepidoptera)
https://en.wikipedia.org/wiki/Leaf_miner