You can put your users signature limit with this hack...
Mark as Installed (http://www.vbulletin.org/forum/vborg_miscactions.php?do=installhack&threadid=166071) - Nominate for MOTM (http://www.vbulletin.org/forum/vborg_miscactions.php?do=nominate&threadid=166071&type=1)
Install
Go to your admin cp, then:
Plugin System -> Manage Products -> [Add/Import Product] -> Select 'product-imzasinirlama.xml' from your computer then press 'Import'...
Kpt - Signature Limit Setting
Go to your admin cp, then:
vBulletin Options -> Kpt - Signature Limit ->