What a great idea, anything that will help a little can surely only be a good thing. It sounds very discreet - with the details being on a card, the driver can obtain the information without the rest of the passengers knowing and the card-holder who suffers from memory loss can go about their business as normal.
I particularly like the idea of the card with: "please wait for me to sit down in case I fall" - superb - the amount of bus drivers who think they are on a Nascar track when pulling away is unbelievable - I struggle to keep my balance and I'm only in my thirties! Good to see that those who need a hand, should they need, have someone who is ready to assist nearby on the buses - wouldn't it be great if this was rolled out across the UK.