Ytx21cn

Your name appears in https://signatures.toolforge.org/reports/www.mediawiki.org as having an invalid custom signature. There is more information about this at New requirements for user signatures/Help. I think the main problem is that you need to un-tick the checkbox in Special:Preferences about treating your signature as wikitext (because there is no wikitext typed in the custom signature box).  You can update your signature in Special:Preferences whenever it's convenient.