This offer is dead easy, and I would imagine that most people going across the pond will go into a Macy's store at some point - you'd be mad not to.
I know it's not strictly a UK deal, but it is useful to know anyway, especially seeing as thousands of people will be heading stateside in the coming months, what with the recent flight offers that were snapped up.
For those of you going to New York, this will be a really useful way of not getting stung on the state tax (which we all forget about at first!), which I think was 8% (so still a 3% saving on top of that)
International visitors can receive 11% off by showing your passport and receiving the 'Welcome International Savings Card', which can be used for 30 days after it is validated. All you need to do is flash the passport, ask for your discount and that's it.
Domestic visitors can also get 11% discount if you can prove you are from out of state too - easily done if you have a hotel address or reservation.
I'm currently working in Delaware, where there is zero VAT and sales tax, so this is an extra 11% of tag prices, which makes everything an absolute bargain. With the £/$ conversion around 1.8 at the moment (and still climbing!), now is a good time to think about buying dollars and going shopping.
I figure as ever, that the deal will go bone cold, because nobody here can benefit in the UK, but if it helps a few people who travel save a few $$$, then my work here is done.
edit: ramraideruk has advised that a similar discount is available at Bloomingdales too - absolutely huge store!