Load Ionicons using MaxCDN. Source: http://briangardner.com/social-media-ionicons/

load-ionicons-cdn-conditionally.php

<?php

//* Load Ionicons using MaxCDN conditionally
add_action('wp_enqueue_scripts', 'customprefix_enqueue_ionicons');
function customprefix_enqueue_ionicons() {
    if (is_category() || is_home()) {
        wp_enqueue_style('ionicons', '//code.ionicframework.com/ionicons/2.0.1/css/ionicons.min.css');
    }
}

load-ionicons-cdn.php

<?php

//* Load Ionicons using MaxCDN
add_action('wp_enqueue_scripts', 'customprefix_enqueue_ionicons');
function customprefix_enqueue_ionicons() {
    wp_enqueue_style('ionicons', '//code.ionicframework.com/ionicons/2.0.1/css/ionicons.min.css');
}