Per consensus, Polish Wikipedia community agreed to remove 'obsolete-tag' from $wgSignatureAllowedLintErrors.
(The next step is going to be setting $wgSignatureValidation = 'disallow' but I'll request it in a month or so).
Link to discussion: https://pl.wikipedia.org/w/index.php?title=Wikipedia:Kawiarenka/Og%C3%B3lne&oldid=73494086#B%C5%82%C4%99dy_lintera_w_podpisach_%E2%80%93_zmiana_konfiguracji_wiki