[tnguy3n]

@ SternFan, thanks for the bug fix, but technically, you don't have to add any additional phrase. There's one typo, $user['allowsign'] , which should be $user['allowsig'] .
I updated the instruction, it should work now.

For those who installed and didn't have it worked, open admincp/user.php,
FIND:

print_yes_no_row($vbphrase['allowsig'], 'user[allowsig]', $user['allowsign']);

REPLACE WITH:

print_yes_no_row($vbphrase['allowsig'], 'user[allowsig]', $user['allowsig']);

@ babolo , it's possible, but it requires addional hack in register.php file.