WordPress at a glance
function is not described

has_site_icon() WP 4.3.0

Whether the site has a Site Icon.

No Hooks.

Return

true/false. Whether the site has a site icon or not.

Usage

has_site_icon( $blog_id );
$blog_id(int)
ID of the blog in question.
Default: current blog

Code of has site icon: wp-includes/general-template.php VER 5.0.3

<?php
function has_site_icon( $blog_id = 0 ) {
	return (bool) get_site_icon_url( 512, '', $blog_id );
}