A birthday card was a card which was traditionally received on one's birthday. In an alternate timeline, Alan Jackson had his daughter Maria sign a birthday card for Andrea Yates. (TV: Whatever Happened to Sarah Jane?)
Susan Foreman had given the First Doctor a birthday card on which she had written "Happy Birthday Grandfather". By his seventh incarnation it was in the TARDIS library, yellowed with age. Its existence was puzzling to Ace, who had learned that the Doctor only had cousins. (PROSE: Cat's Cradle: Time's Crucible)
One year, River Song received 647 birthday cards from the Doctor, at various points in their timeline, but on her other birthdays, she received nothing. (AUDIO: R&J)