Ban particular senders from having text appear in lockscreen My bank uses "smsTAN", so when I make a transfer, the TAN gets texted to me. I would like to prevent texts from my bank from appearing in the lock screen as this lowers the safety of this method (someone would just have to nab my phone and find out my five-letter online PIN, don't ask me why my bank still enforces five-letter PINs). 

I'd like to keep my other texts appearing in the lock screen.
Although excluding specific contact's text from being shown on the Lock Screen is not possible, you could always switch off the Show Preview option. Therefore a notification of your bank will be shown, but no portion of this message will be previewed, safeguarding your five-letter PIN.

To do so just go to Settings / Notification Center / Messages and turn off Show Preview.