Is there an option for an Amazon Seller to add a Promo-Code field on an Amazon Page ?

I wonder if something like exists or is offered to me as an option to use. As I get my Amazon store front set up, I think it would be very helpful to me and customers if I had the ability to include place on the page where someone can enter a promotion code or the name of someone who referred them to my product. The intention of this is to offer word-of mouth-advertising. I hoped I am explaining this feature using easy to understand terminology. Let me give you an example. You hear from time-to-time in a commercial on the radio or even in an ad on a web site to "add promo-code..." in order to get a discount or something. This, I assume, is a way to track the effectiveness of advertisement and which advertisers are doing a good job at driving traffic. That would…