This is a Unity asset that mimics The Mark of Communication from Rain World. I made it for use on my copy of wab.boi's scavenger avatar (which I quite like). The mark can be recolored to any color you want, and has an optional pulsing animation to make it fade in and out like it does in-game.
This is another one of those comically simple effects I created which is so simple that it makes no sense to charge for, so it's yours free unless you choose to donate.
Details:
This is the asset. Requires VRChat SDK to be installed.
Version 3: Rotation constraint is no longer required; the shader corrects for rotation inline.