Hello, this is my solution for this problem:

else if($meta['e_type']=="URL") {
            if(osc_field(osc_item_meta(), 's_value', '')!='') {
                if (strpos(osc_field(osc_item_meta(), 's_value', ''),'http://')===false) {
                	return '<a target="_blank" href="http://'.htmlentities(osc_field(osc_item_meta(), 's_value', ''), ENT_COMPAT, "UTF-8").'" >acessar >> </a>';
                } else{
                	return '<a target="_blank" href="'.htmlentities(osc_field(osc_item_meta(), 's_value', ''), ENT_COMPAT, "UTF-8").'" >acessar >></a>';
                }

Bye bye! Miguel Urtado