The Readme says "marketing", not "advertising". While the Wikipedia definition of "Marketing" is the biggest collection of hot air I've ever seen, I gather, somewhat, that "marketing" refers to trying to determine your customers wants and needs so as to profitably serve them. (Whereas "advertising" is trying to change the customer to fit the company's needs.) So, maybe, it refers to polls? But then they already had the ability to conduct polls in-game.
Maybe as you are plummeting towards the ground a billboard appears in-game saying "Would you like to buy another wing? Only an extra $5. Act now before you hit the ground." 
Technically marketing includes anything that enables the sale of a product or service to a customer which, among other things, could include branding, product development, distribution strategies, advertising, merchandising, sales, customer service and much much more.
