Route directly to an S3-hosted asset?
By default browsers look for a favicon at the root of your web directory. So if you do not add a link in your head section, but you have a favicon.ico at webroot, you will still see it.

However, a favicon can technically be located anywhere. If you have a multi-site installation you can reference it like this (note that you should always use a fully qualified URL or you may run into issues with IE):

&lt;link rel="shortcut icon" href="https://yourbucket.s3.amazonaws.com/{{currentSite.handle}}/favicons/favicon.ico" type="image/x-icon"&gt;


Insert Craft's current site handle tag so that you can use the same code on all sites. Then you'll just need to create a paths in your S3 bucket to match.

Regarding multiple sizes, you should include more than just a 16x16 favicon. This is what I have which is all related to icon display:

&lt;link rel="shortcut icon" href="favicon.ico" type="image/x-icon"&gt;
&lt;link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png"&gt;
&lt;link rel="icon" type="image/png" sizes="32x32" href="/favicon-32x32.png"&gt;
&lt;link rel="icon" type="image/png" sizes="16x16" href="/favicon-16x16.png"&gt;
&lt;link rel="manifest" href="/site.webmanifest"&gt;
&lt;link rel="mask-icon" href="/safari-pinned-tab.svg" color="#888888"&gt;
&lt;meta name="msapplication-TileColor" content="#ffc40d"&gt;
&lt;meta name="theme-color" content="#ffffff"&gt;


The manifest, mask-icon, msapplication-TileColor, and theme-color all refer to how your favicon will appear on platforms including Safari, Windows and Android devices.

You could add an image transform to your asset volume which creates each of the required sizes, or you could direct your client to upload multiple sizes. It may be easier to send them to this site to generate favicons which they can then upload to their assets volume.

Disclaimer, I have no affiliation to the Favicon Generator site -- I just use it frequently. I generated the code you see above using this tool. If you're looking for a reliable way to generate your favicon size variations and the associated code, this online tool does the trick.