Here's the info from the mailer. There is no promo code.

Here's the text of the outside flap:
Earn double miles until 2005! Just use your Mileage Plus Visa.

Inside, top flap:
From October 1 through December 31, 2004:
Earn Double Miles until the end of the year.
Re: your account ending in xxxx
Use your Mileage Plus Visa card to make purchases in any of these categories-->
(off to the right)
Dining out
Groceries
Gasoline
Utilities
Dry cleaning
Wireless phone service
Drug store
Movies & refreshments
Video rentals

You'll earn double miles for every dollar spent above $250 each month for these purchases.
That's in addition to the miles you already earn on all other purchases. So now is a great time to use your Mileage Plus Visa for all kinds of everyday spending. In no time, those Double Miles can add up to a fabulous vacation.

Watch Your Miles Add Up!
Every dollar spent above $250 in these categores: Double Miles!

(Bottom half of card):
There's no need to enroll. Just use your Mileage Plus Visa.

That's it, aside from the footnotes and small print.
There is no promo code.