The UK routinely accepts passengers with foreign passports that are not signed. In many instances, the UKBA has little to no choice but to accept the foreign passport as presented unsigned.

In place of where the signature of the passport holder would go, UKBA often runs across the words "not able to sign" or something of the sort in the passport.

The US and Canada also routinely accept such foreign passports that are not signed; and if those passports were signed, it could well be considered defacement of the issuing authority's property.