Modified from the icon at https://scp-wiki.wikidot.com/anomaly-classification-system-guide, which was licensed under CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/), and accordingly I'm distributing this modified version under the same license.
The original icon is the work of SCP content creator Woedenaz (http://www.wikidot.com/user:info/woedenaz).

The change I made was only to fill the "blank" parts of the icon with white so background colors would not show through.  All meaningful credit is to Woedenaz.
Own work
Shawnomancy