Seriously, when asked
Could you give us as much info as possible on all your security measures?
and
We had it audited by a bank auditing company. It exceeds banking compliance standards.
you can't do better than
Everything is encrypted with high grade encryption, salted.. etc etc.. Comodo "green bar" SSL, firewalled...
and
oh Trust me...

BTW: PCI Compliance is a complete crock of dog poop. There is no standard testing procedure and the tests performed are often outdated and crazy picky about some things while compeltely ignoring other important things. It's all a sham to make money and worse than TSA's security theater at the airport. Website disappears with a 404 error because they deleted the page?? Not confidence inspiring.