In this December 2023 RFC, the English Wikipedia chose to disallow obsolete tags in newly saved signatures.
In task T140606, matmarex wrote "I updated the patch to include a config variable $wgSignatureAllowedLintErrors. It defaults to [ 'obsolete-tag' ] (which allows <font> tags etc.), and you can file a task to change this config to an empty array [] whenever the community of English Wikipedia (or any other wiki) agrees to that."
This task is requesting implementation of the RFC's consensus via removal of 'obsolete-tag' from $wgSignatureAllowedLintErrors on the English Wikipedia.