Lightning's Fingerprint

Sometimes, under the right conditions, a high-voltage electrical discharge will create a cool fern-like pattern called a Lichtenberg Figure (named after Georg Christoph Lichtenberg.)

They are found in sand when lightning strikes. (called fulgurite)
They are found on the surface of water in 300 trillion watt pulse generators.
They are found on human skin when lightning strikes.
They are found in lawns where lightning strikes.
They are found in chunks of polymethylmethacrylateacrylic (acrylic) that you can buy here.