I don't think there is a way around it. If a spectator signs a card they should keep it as a souvenir which leaves the magician one less card in the deck. Even though the deck doesn't have all 52 cards, it is a sacrifice for the craft and the spectator's experience.
About a year ago I did some magic at a homecoming dance and I had a girl sign a card for "Here then There." She was blown away and I let her keep her signed card, and she brought some of her friends for me to perform for resulting in more performances throughout the night. Three weeks later I saw that she kept her signed card in her PHONE CASE!!! To the best of my knowledge she still has her signed card in her possession.
My best suggestion for
@davider7396 would be to use Bicycle decks and have the spectator sign their card and keep it, then use the deck for signed card tricks until the deck is about 45-40 cards thick and then switch to a new Bicycle because they are affordable. If you can't afford going through signed cards then don't do signed card tricks until you can afford to replace decks.