You can't tell from the signature itself, but one big group of people got caught with a vaccination record entered into the system from a company that exclusively takes tests.
I don't know the exact methodology the government uses to catch fraudsters, but from someone who just scans the certificates there's no way to find a fake record.
That is, a fake record that matches the person's ID card details. Here in the NL, that's your initials and your partial birthday. Most abuse is people using other people's certificates, which can trivially be caught by checking the necessary identification, as you're told to by the scanning app anyway.
