Advertising should be able to say something like "Click this link for a 15% discount!". Then the URL would be something like www.mysite.com?cc=dis15. Then on checkout, the coupon code field would be prefilled with dis15.
Actually, the feature kind of exists but is almost useless as currently implemented. The URL is www.mysite.com?coupon_code=dis15. The problem is that the landing page can only be the sign-up form for a specific plan. When the potential customer goes to any other page the coupon code is lost.
It is useless when more than one plan is offered (ie 100 records, 250 records, 750 records, etc) because a customer should land on a page that provides those choices. Even if there is only one plan choice, the link bypasses all service explanations so the customer will usually want to go to another page to learn about the service first. That would annoy many potential customers and lose sales.
Couldn't cookies be used to preserve the coupon to allow any landing page?
A nitpick is that the parameter name would be better if shorter. It is currently "?coupon_code=dis15". I would prefer "?code=dis15" or "?cc=dis15".
