WordPress at a glance
function is not described

site_icon_url() WP 4.3.0

Displays the Site Icon URL.

No Hooks.

Return

Nothing (null).

Usage

site_icon_url( $size, $url, $blog_id );
$size(int)
Size of the site icon.
Default: 512 (pixels)
$url(string)
Fallback url if no site icon is found.
Default: ''
$blog_id(int)
ID of the blog to get the site icon for.
Default: current blog

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

<?php
function site_icon_url( $size = 512, $url = '', $blog_id = 0 ) {
	echo esc_url( get_site_icon_url( $size, $url, $blog_id ) );
}