[RedTyger]

You could use a switch if you wanted it to be a little neater I suppose, I personally would use THIS_SCRIPT to determine when links are used as the other variables may be added or used elsewhere.

switch (THIS_SCRIPT)
{
case 'member':
    $headinclude .= '<link rel="meta" type="application/rdf+xml" title="SIOC" href="sioc.php?sioc_type=user&sioc_id='.$_REQUEST['u'].'" />';
    break;
case 'showpost':
    $headinclude .= '<link rel="meta" type="application/rdf+xml" title="SIOC" href="sioc.php?sioc_type=post&sioc_id='.$_REQUEST['p'].'" />';
    break;
case 'showthread':
   $headinclude .= '<link rel="meta" type="application/rdf+xml" title="SIOC" href="sioc.php?sioc_type=forum&sioc_id='.$_REQUEST['t'].'" />';
    break;
case 'forumdisplay':
   $headinclude .= '<link rel="meta" type="application/rdf+xml" title="SIOC" href="sioc.php?sioc_type=forum&sioc_id='.$_REQUEST['f'].'" />';
    break;
default:
   $headinclude .= '<link rel="meta" type="application/rdf+xml" title="SIOC" href="sioc.php?sioc_type=site" />';
}

You can clean the $_REQUEST values if you want, but as they're not accessing any data and the forum will deal with incorrect values by default it's probably not necessary.