This effect sound interesting.
If you have it let us know what you think about it.

https://www.lybrary.com/the-dark-card-p-925470.html

Effect:
From a red-backed deck, a spectator selects and removes a card, signs the face, and returns it to the deck. The deck is spread and a blue-backed card is seen in the middle of the spread. When turned over, it is the card he signed.

Remember:

The spectator removes and handles his initial selection which is a red-backed card.
At the end, he can also handle the blue-backed card (he can even keep it as a souvenir).
No carbon or other signature transfers. This one is a fooler. It is one of those "things that make you go unhhh?"

It is a cool trick and quite a fooler. A great alternative to Chicago Surprise. If interested, consider getting this as well:

https://www.codyfisher.com/product-page/magic-card-wand

You get a good repositionable glue stick along with a bunch of routines, including the Dark Card. And of course some sort of glue is needed to make the gimmick. I don't know if shipping to Sweden would make it impractical. But the e-book will go into much more detail.

Watch a performance of it by Jean Boucher himself starting at 26:50