There is no requirement in the writing of a fictional correspondence that a postcard must be only fictional. The making of these things is entirely a matter of what the author feels like at the moment. For instance, the postcard below which I recently sent off.
On its back is a pleasant note to a very real friend. She had written me of late, on a very odd stationery; "paper" that was actually made of plastic. I was replying to thank her for an article she'd sent and to comment on a book she had recommended and that I had finally obtained in hardcover.
Aside: It is my belief that good books ought to be read in their finest form which, to me, is a cloth-bound item with exceptionally good quality paper for its pages. I have used PC Kindle to read and find it unsatisfying mostly because a laptop screen is ill-configured, ergonomically and optically, for recreational reading. I hope, someday, to try a real Kindle -- or Nook -- and then see what I think of ebookery.*
On the front of the postcard I have taken the opportunity to record four different tales - or implications that might form tales.
Tale 1 (bottom of frame): Left disconsolate by the herd's rejection of his time-travel roller skates invention, Tycho sought a solitary refuge deep within the forest unaware his future selves hovered nearby. (Thereby disproving the time travel paradox of meeting oneself.)
Tale 2 (top of frame ): The trees, whose lifespans could be measured in millennia, had heard it all before and felt sympathy for the young therapod.
Tale 3 (left of frame): [The forest was a silent place.]
Tale 4 (right of frame): [In future eras, the red moss would be used to dye the court robes of royalty.]
* My day job sees me using a computer quite a bit, however, so leisure reading on a machine does not appeal to me aesthetically.