Manual:$wgSignatureValidation

Details
Behavior of signature validation. Allowed values are:


 * 'warning' - invalid signatures cause a warning to be displayed on the preferences page, but they are still used when signing comments; new invalid signatures can still be saved as normal
 * 'new' - existing invalid signatures behave as above; new invalid signatures can't be saved
 * 'disallow' - existing invalid signatures are no longer used when signing comments; new invalid signatures can't be saved