I do not know if it’s true for all countries, but at least the USA and the UK require your passport to be signed to be valid. And I know that when I fly, I sometimes get checked if it is signed.

Is there a practical reason for this? Does the signature get checked against anything? Or is it simply that the law says a passport must be signed to be valid, so there you go?

I googled around a bit, but only found resources on how to sign, but not why it needs to be signed.

Thank you Internet hive mind!