Anonymous and temporary users' signatures are formatted using the signature-anon and signature-temp messages. They are marked as "ignored", which means that they are not translated on translatewiki, although they can be locally customized on the wikis. And indeed, signature-anon was customized on the Hebrew Wikipedia: IP addresses that appear between RTL text and dates may appear in the wrong order, so an interface admin added the RLM control character.

This solves the problem, but only for the Hebrew Wikipedia, and not in the most robust manner possible. It would be better to do it for all the wikis, and with something more readable than a control character. The {{BIDI}} magic word can be used for that, and it should be done in the code, so that local wikis wouldn't have to customize it.

It's useful for temporary accounts, too.

(This is not necessary for logged-in users because they can change their usernames or signatures if they cause problems on talk pages, but anonymous and temporary users can't.)