For joint accounts 3 criteria needs to be met. The 3rd concerns me as we use a universal signature card.
All co-owners must sign the deposit account signature card unless the account is a CD or is established by an agent, nominee, guardian, custodian, executor or conservator

At our bank, each customer has one signture card on the card it says:"If more than one person is named in the title for any account, such account will be considered a joint account. Instructions which affect any of my joint accounts may be given by any joint account owner." But nowhere on our cards does it list joint owners. The way our card works is that each account is governed by the account title on the account. So I have one "signature card" on file and may 3 different accounts: a single ownership account, a joint account with a spouse and another with a child. Not that we are looking at an FDIC takeover but do we have a huge problem that we need to fix for our customers.