This page shows the different variations of the Thunderbolt from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free. Icons are available in PNG and vector.
The icon is a logo of Thunderbolt. The icon has a bunker like shape, with what appears to be a long horizontal rectangular window in the center. There is also a lighting bolt with an arrow on the bottom of it, located directly on top of the bunker shaped object.