You can use an emoji as a favicon with this simple snippet:

<link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 100 100%22><text y=%22.9em%22 font-size=%2290%22>🎯</text></svg>">

Credits to CSS-Tricks for this snippet.