Got an emails from BA stating:

Add an authorized user to your British Airways Visa SignatureŽ Card and you'll receive 5,000 Bonus Miles.1 Simply add a family member or friend and you'll earn BA Miles every time they use their card.

HERE'S ALL YOU NEED TO DO.
Log into your account at Chase.com/addcard to add an authorized user.2 Then you'll start earning miles every time your friend or family member uses their card!

TERMS AND CONDITIONS:
1 Additional cards and all cardmember communications will be mailed to the primary cardmember, who is responsible for all charges made by the authorized users. Reference to the account may appear on the authorized users' credit reports.

2 You will receive your bonus if you meet the requirements specified in this offer. Please allow 6 to 8 weeks after the last day of the promotional period for bonus rewards to post to your account. Bonus rewards earned from this promotional offer will not count against any maximum reward accumulation in the rewards program, if applicable. Credit card product changes during the promotional period will forfeit this bonus offer. To qualify for this bonus offer, account must be open and not in default at the time of fulfillment. This promotional offer is non-transferable and applies only to the account ending in the last 4 digits referenced in this offer.

3 See Rewards Program Rules and Regulations for details.

BA Miles earned on the credit card by the authorized user, who is the primary cardholder, will be credited to the Executive Club membership attached to the card, regardless of whether any secondary users have another existing Executive Club memberships with British Airways or belong to our Household Account programme.