This is 100% woocomerce, before messing it with custom CSS you should check or ask if they have an option to not have the icon.
The icon is added with the rule below
.woocommerce-error:before,.woocommerce-info:before,.woocommerce-message:before{
font-family:WooCommerce;
content:”e028″;
display:inline-block;
position:absolute;
top:1em;left:1.5em;
}
So you could hide it with
.woocommerce-error:before,.woocommerce-info:before,.woocommerce-message:before{display:none;}
But it may remove it in place you don’t want