Oystercard for those who don't know is the modern ticketing system used in London. It's a "swipe" card you can use on buses and the underground.
Anyway, I registered on their website today and it starts like any other registration form with the desired username and password. When I submitted the first form it gave me an error message shown in this picture
"Your password needs to be at least six characters long and contain a mixture of uppercase and lowercase letters and at least one digit. For example, Abc123."
Have you ever seen that before? Stupid! The password I first intended to use is only a mixture of lowercase letters and several numbers, which works perfectly fine on UNIX. The effect was that I had to come up with a new one which I'll probably forget sooner or later. To avoid forgetting it I have written it down on a small piece of paper here on my desk. How's that for security?