I'm not sure where this whole signature being checked by the bank is coming from.
Under the Irish 'DD plus' scheme, you don't need a signature on a mandate if it's an Irish IBAN and a DD+ originator. No signature or paper mandate is required by anyone.
Even if it's not a DD+ originator, the mandate never goes near the bank. All SEPA DDs are just electronic messages. The originator keeps the mandate.
However, the originator has signed up to a set of rules that provides the account holder huge protection, and unauthorised DDs can be reversed for up to 13 months.
An originator needs a bank sponsor before they can raise DDs, so in the event that they're not able to refund, then their sponsor bank pays.