Two different methods to mark Bicycle Rider Back / Bicycle Standard playing cards.

Nothing tough to memorize.
You'll literally be doing it in minutes after reading this eBook.

Pigment : You can identify the card from upto 4 feet away (depending on lighting conditions).
Deck looks completely normal during ribbon spread and riffling the edges.
A whole deck can be marked in less than 10 minutes.

Pixel : Directed more towards close-up situations, ideal range for reading this up-to 3 feet. Marks are on the outer side of the back and is available from all the four sides.
(One cannot riffle through the edges to prove the deck's innocence, however riffle force is possible)
Marking a full deck will take upto 20 minutes.