its not really, its basically the same as fake paper shares from the late 17th century. Sure everyone knows they are fake, but they still have a value because they can talk a good game.
"I've just sold 15 shares in the south sea company to Jacob, I have a few left, I can do you a good price."
but how do I know they are real?
"look they have the seal, and they are numbered. plus shares only give you a tiny part of the company anyway, its totally new and valuable. The prices keep going up, you can sell them to your friends"