Hip means trendy and fashionable. Of course, Un-hip is the opposite. Since Shreve Crump & Low is considered a conservative jewelry store, this ad wants to show people they can be stylish, too.
"Lest anyone dare to refer to us as unhip..." means "In case anyone has the courage to say we are not fashionable..."
Yeah. Look at this strange necklace! We're not just for engagement rings anymore!!
Advertisement in The Improper Bostonian magazine October 16, 2002