For a limited time, select American Express cardmembers are eligible for the following promo: Spend a total of $5 or more on iTunes using your enrolled American Express Card by April 30, 2014, and you’ll receive a one-time $5 statement credit.

To see if your card is eligible for this offer, log in to your American Express account online and click on the “Offers for You” tab towards the bottom of the page. If the iTunes offer is listed, click the “Save Offer” button next to it to enroll your card in the promo.

Full offer terms are as follows:

Offer valid only for iTunes purchases; not valid for any other purchases of Apple products in-store or online. Offer valid only for purchases made with your enrolled Card. Please make sure that your enrolled Card is the payment method set for your iTunes account in order to redeem the offer. Enrollment is limited. Offer is non-transferable. Limit 1 statement credit per American Express online account. If you order an item during the offer period but it is not provided until after 4/30/14, it may not count towards determining whether your purchase qualifies for the offer. Statement credit will appear on your billing statement within 90 days after 4/30/14, provided that American Express receives information from Apple about your qualifying purchase. Note that American Express may not receive information about your qualifying purchase from Apple until all of the items from your qualifying purchase have been provided by Apple. Statement credit may be reversed if qualifying purchase is returned/cancelled. If American Express does not receive information that identifies your transaction as qualifying for the offer, you will not receive the stmt credit. For example, your transaction will not qualify if it is not made directly with Apple. In addition, in most cases, you will not receive the stmt credit if your transaction is made with an electronic wallet or through a 3rd party or if the merchant uses a mobile or wireless card reader to process it. POID: AZZN:0001

At this time, it unfortunately doesn’t appear that there is a way to sign up for this offer through Facebook or Twitter if you were not offered it in your American Express online account.