$a=array(0 =>array([logo] => array
                (
                    [id] =>1
                    [sid] => 6
                    )
    1=>array([logo] => array
             (
            [id] =>2
             [sid] => 6
              )
)
使用foreach循环$a，只显示不同的sid；
回复讨论(解决方案) 贴出经var_export() 运行后的数组出来
$last = 0;foreach($a as $r) { foreach($r as $v) { if($last != $v['sid']) echo $v['sid']; $last = $v['sid']; }}

array ( 0 => array ( 'logo' => array ( 'id' => 1, 'sid' => 6, ), ), 1 => array ( 'logo' => array ( 'id' => 2, 'sid' => 6, ), ), )
$res = array();foreach($a as $v){ if(!isset($res[$v['logo']['sid']])) $res[$v['logo']['sid']] = $v;}print_r(array_values($res));

$last = 0;foreach($a as $r) { foreach($r as $v) { if($last != $v['sid']) echo $v['sid']; $last = $v['sid']; }}

刚刚测试了下，表示您给的代码有点缺陷，改良了下：
$i ='';
foreach($a as $r=>$v){
foreach($v as $k=>$vv){
if(!stristr($i,$vv['sid'])) {
$i .= $vv['sid'];
echo $vv['sid']; } } }应该没有什么问题了
$res = array();foreach($a as $v){ if(!isset($res[$v['logo']['sid']])) $res[$v['logo']['sid']] = $v;}print_r(array_values($res));

可能我问题说的不清楚，不过还是解决了，主要是去掉同一字段的重复的结果。