Many years ago I used to work for a Bank and one day we had a phone call from another of our branches saying one of our customers was in there and wanted to withdraw �1000 cash, which they weren't happy to do as obviously they didn't know him from Adam. Luckily this was one of our more 'popular' customers, so to identify him we said they should ask who he had sent valentine cards to a couple of weeks earlier. They said he'd burst out laughing when they'd asked the question and answered correctly, Jill and me, so they let him have the cash!
As many less people go into their branches these days and are therefore not really known by their branch staff I suppose a pass code is a good idea.
By the way Hermia, if we needed to identify other customers we usually asked them things like when did they open their account, what standing orders have they got, things that other people couldn't guess!