This task is about fully deprecating signatures that will be made invalid by the following changes:
//The patches to implement the "Requirements" described below should NOT be merged until the following tasks are resolved://
//Draft; @ppelberg needs to finalize these.//
- When someone attempts to save a signature (`~~~~`) to a page that is made invalid by the changes listed above, said "signature" should be replaced with that wikis' default signature.
- When someone attempts to set a custom signature in `Special:Preferences` that is made invalid by the changes listed above, they should see a message that informs them:
- The signature they've entered cannot be saved
- The reason(s) why that signature cannot be saved
- What they can do to make their signature valid
=== Open questions
- [ ] When should this change be made?
//For more details, see the "Implementation plan" described in T248632.//