Just got my copy yesterday, so first of all....THANKS! I just finished reading through the rules and then looked at the components and wondered, "What are each of these thick stockholder certificates for?" I didn't recall reading anything about them, but in my excitement, I may have breezed right by it.
They were a stretch goal funded during the Kickstarter that serves two purposes (in my mind):
1) Place them next to the board to remind players that majority shareholder bonuses are worth $10K at the end of the game.
2) Reward players with something at the end of the game to indicate they had actually received the majority bonus and avoid "oh i forgot to get that" moments.