American’s small business ‘double dip program’ has its own credit card. American Airlines actually has a co-brand card issued by American Express.
I use the program and have redeemed points to gift Gold elite status in AAdvantage and Admirals Club memberships, and I usually keep a stash of (paper) upgrade certificates on hand.
I mentioned the program’s credit card several years ago. I don’t recall it ever having a signup bonus. But it does now.