<svg xmlns="http://w3.org/2000/svg" viewBox="0 0 100 100">
<text y=".9em" font-size="90">👾</text>
</svg>
Reference:
Now that all modern browsers support SVG favicons, here's how to turn any emoji into a favicon.svg:
— Lea Verou, PhD (@LeaVerou) March 22, 2020
<svg xmlns="https://t.co/TJalgdayix" viewBox="0 0 100 100">
<text y=".9em" font-size="90">💩</text>
</svg>
Useful for quick apps when you can't be bothered to design a favicon! pic.twitter.com/S2F8IQXaZU
More description SVG favicons and favicons maintain general: