Several characters in Zero History e.g. Milgrim and Heidi, take journeys on the London Underground Tube system.
Here is an image of a Transport for London Oyster Card - prepaid London Underground Tube and Bus travel card (but also a RFID / centralised database tracking and surveillance system) signed by William Gibson, at Forbidden Plant, London, Saturday 9th October 2010,
To protect your privacy and personal security from 13.56 MHz licence free Industrial Scientific Medical radio frequency band snoopers (both legal and illegal). You can disable the passive radio tracking behaviour of these cards by simply lining their plastic wallets, with some aluminium cooking foil. which stops the embedded antenna loop from powering up the microchip. The same sort of protection is also needed for RFID "biometric" Passports.
There is also the practical issue of preventing accidental deductions of money from your Oyster card, by maladjusted or poorly maintained or hacked Card Readers. These are normally specially de-tuned to have an effective range of only a couple of centimetres. However , the radio equipment, in order to comply with the international standards and markets, is actually designed for Portals or Doorways i.e. a couple of metres range, even without illegal amplification.
There have been times when the narrow London Underground turnstyle gates have picked up signals from someone going through a gate on either side of them, thereby secretly deducting money from the prepaid card, even when someone has been using a paper ticket, and has had their Oyster card still in their pocket.
Using the Oyster Card, leaves a financial and time / location database transaction trail, which is used anonymously in bulk, to help Transport for London optimise their services.
However this data has been specifically exempted from the Data Protection Act 2000, by Ministerial fiat, under the previous Labour government, and is now handed over, "in bulk, in real time", together with the tens of thousands of CCTV surveillance camera live feeds or recordings, which infest the London Tube and Bus systems, to the Metropolitan Police Service, for mass surveillance database mining, in secret, for "suspicious" travel patterns. This sweeps up the innocent travel patterns and other data of millions of innocent people, as well as the alleged "terrorist suspects" which justify this policy.
However, some "cyberpunks" etc., have for years, been trying to frustrate this sort of "Big Brother" snooping on individuals, by regularly swapping their Oyster cards with friends or acquaintances, something which does not affecting the legitimate aggregated, anonymised bulk travel pattern data uses, which Transport for London might need to improve their services to the public.