Pin codes are user specific discount offers mailed or emailed out to potential guests in an attempt to induce them to book trips at WDW. The 15-digit code is somewhere on the message, usually at the bottom or somewhere near the pricing information. You have to cite that code to the reservation agent in order for it to apply. Some have reported success in calling and asking if they have a code attached to their name; others have not. But if you have a pin and intend to use it, you must mention it or you won't get the discount (unless the CM takes pity on you and tells you about it).
You could try the usual attention getting steps -- register an email address with the formal Disney site, fill in the profile information and check yes to everything they offer in the way of information and promotions. Then order the annual WDW planning DVD, which comes by post, and often triggers a number of emails based on that expression of interest.
Then go back to the Disney main site, log in, and price out and save for later several trip options including dining, rooms and tickets. Go back and review them within several days and then change some of the options.
If you get a pop-up survey, be sure to answer "considering travel, but looking for better value" or "too expensive at this time" in the radio button options.
When you get emails offering you an opportunity to customize maps or play online games or download trip planning apps, do it. Anything that increases your interactivity with the Disney site shows up in the marketing department's "Fairy Godmother Department," and that can only help.
None of these techniques are guaranteed to win you the pin prize, but these techniques have been reported in the past to have been used just prior to receipt of pin codes.
Also, there are other tips and tricks concerning pin codes in the sticky up above...
I've done them myself; I have two codes thus far this year...
Your mileage may vary. Good luck!