According to news reports from the USA it means 'Buy American, Hire American' but then source all your MAGA baseball caps from China
The Metro contained the following quote from a Trump supporter - read via the full story via the link below to the newspaper:
Rob Walker, 44, who had driven to Washington from Georgia with his wife Abby, 36, had stopped at a truck stop on the way to buy a ‘Make America Great Again’ cap.
‘Oh God, I hope it’s not made in China,’ Abby said, flipping the cap over to check. She looked at its label. ‘China! Don’t tell anyone!’
Read more: http://metro.co.uk/2017/01/22/donald-trump-supporters-find-out-their-hats-werent-made-in-us-6398848/#ixzz4WcvM4ImU