Surely everyone gives a sample signature when they open a bank account. That being so, then all they need to do is scan that signature into their system and hey presto they have a digital record.
I have read elsewhere that other documentation is needed.
I checked with my bank and they said if a customer, who is not resident, and thus will not have produced an EU Citizens Registration Cert, must produce their current passport if it has been renewed since opening the account.
I am sure each bank will have it's own interpretation of what, if anything, is required.