In Mad Men episode 7.08, Severance, Don’s date finds Megan’s earring under the bed. It looked familiar, so I did some exploring.
In fact, Megan wore this pair of earrings twice that I can discover, in two consecutive episodes of Season 6: To Have and To Hold, and The Flood. This is great work by Janie Bryant. These earrings were favorites of Megan’s for a while, and then she lost one. We never see her wearing them in Season 7, so the continuity–she lost them before she moved to California–is perfect.