Has anyone tried to use a Capital One chip and signature card for contactless payment on the tube and did it work?
The chip & pin/signature and the contactless chips are separate chips. Chip & pin cards don't automatically include the contactless feature, you'll have to contact Capital One to find out if your card has both chips. The contactless chip is buried in the middle of the plastic of the card and can't be seen with the naked eye.
FWIW, my paypass debit card did work at the London metro stations, the official site says that cards issued outside the UK may or may not work. It's an awesome service, you don't have to deal with the Oyster cards. I'm gonna be in London next week and I'am going test out the contactless Apple Pay feature on my Iphone.
A card with contactless capability will have a symbol on it to indicate it. On the card pictured at the link below it's on the upper right corner.
I've had problems using 'contactless' on the tube, and if you do have a problem, the tube staff can't fix it as they cannot access your bank card info. I now only use a proper Oyster Card.