National Rail logo, then you show the rail pass along with the printed vouchers. (I don't know why they still require the printed vouchers, but that seems to still be the case) Most everything on their site is 2 for 1 or better.
Days Out discounts:
London Eye (meh)
Tower of London (Ceremony of the Keys is already booked through April 2020, but cancellations come up)
St. Paul's
Churchill's War Rooms
Hampton Court Palace
Globe Tours
I really enjoyed the Imperial War Museum (free)