Schema module reports the warning mentioned on the issue title.

To fix, edit signup_status.install, and apply:

 function signup_status_schema_alter(&$schema) {
   $schema['signup_log']['fields']['status'] = array(
     'type' => 'int',
     'not null' => TRUE,
-    'default' => '0',
+    'default' => 0,
     'description' => t('The status status.'),
   );
 }

Cheers