Just wanted to add that I was able to use my Hyatt Chase card successfully in London to add value to my Oyster card via a kiosk. My first try was rejected, but luckily there was a helpful agent there who told me that foreign cards would only authorize transactions < US$25 (I had tried to top up £20). When I changed the amount to £15, the machine accepted the transaction, no signature needed.
I also used my card at a restaurant in London and had no problems with it. The server took my card, used the chip, and then had me sign the paper that it produced. So definitely chip+sign worked as well with the card.