Forumlar / Cotonti / Extensions / Own Plugin Tag in BEGIN: USER

I want to set a TAG in the Template in the Part:
<!-- BEGIN: USER -->
{MY_PLUGIN_TAG}
<!-- END: USER-->

The Tag is in my Plugin.header.php

[BEGIN_SED_EXTPLUGIN]
Code=sociallike
Part=main
File=sociallike.header
Hooks=header.tags
Tags=header.tpl:{SLHEADER_SOCIALLIKESTART}
Minlevel=0
Order=11
[END_SED_EXTPLUGIN]

...

$t->assign("SLHEADER_SOCIALLIKENEWS",$itsactive);
$t->assign("SLHEADER_SOCIALLIKESTART",$START);

Can anyone help me?