When my wife can’t remember someone’s name, she’ll grab my hand and squeeze it with two quick squeezes “Help. Me.”.
That’s my cue to either work their name into a comment/question or, if I don’t know them, introduce myself followed by a “And you are…?”. Works pretty well all of the time.
Of course, being together so long, and loving to fuck with each other’s heads when we can, sometimes I’ll just stand there and give them my best Aussie “owzitgoin?”, and watch my wife squirm. That’s usually when the nails dig into my hand, hoping to draw blood.