Here are some tips on how to mark cards, and even better, how to find the scammed cards:
The marks can be found along the uppermost border of the pattern on the back of the card. Running crossways the top you can see ten "sprout" drawings. The two sprouts located at the center predetermine the rank. There are six leaves on each sprout. To show the rank three on Ace, a leaf is disjointed with a blob of ink on or after the sprout.
From the bottom, up to the top the leaves positioned left from the middle sprout indicate queen, king, and ace. 9, 10, and jack are marked by leaves situated right from the left sprout. Likewise, cards 8 to 3 are indicated on the right middle sprout. The card is named a deuce, when no leaf is detached. On the left side of the middle sprouts, there are 3 sprouts forming a suit. Hearts, clubs, and diamonds are represented by the partially blocked "bud" on the uppermost side of the sprout. You have a spade when all of the buds are complete. In order to read the cards from both ends, the markings recur at the bottom.
Look for the angel in the higher left angle. You will see his left hand resting on a climbing plant that surrounds a flower with eight petals. The rank is indicated by the flower. A card is an ace when the higher (twelve o'clock) petal is reduced. Clockwise, the place of the reduced petal indicates king at one thirty, queen at three, jack at four thirty, ten at six, nine at seven thirty, eight at nine, and seven at ten thirty.
For inferior ranks, the internal edge of the petal is thickened. Six is a scammed petal at twelve o'clock; five is at three; four is at six; three is at nine o' clock. Every petal is complete for the deuce.
A leaf with three parts is designed atop the arm. A mark on the left part of the leaf means heart. For clubs, the mark is on the middle part, whereas for diamonds the mark is on the right part of the leaf. Spades are not marked.
On every bee card a line of diamond motifs runs just within the right border. The rank is shown by the top 3 full diamonds. See the top of these diamonds. Ace is indicated by a triangular elongation of black ink on the right of the diamond's extreme point. A king is recognizable by a mark on the uppermost left side. Same marks on the lowest point denote jack, if it's on the right, and queen, if it's on the left.
Cards 10 to 7 are indicated by the diamonds below the queen, and cards 6 to 3 below the jack. Deuces are unmarked. On top, to the left of the superior diamond, there is an additional full diamond. It marks the following suits: uppermost right means diamonds, clubs are on the uppermost left, and hearts are on the base left. Spades are unmarked.
A trained eye reads immediately the aviator or the Bicycle. It is trickier to read the Bee. It might take a few minutes to spot the markings, especially if their location is unknown.