Notch On One's Bedpost Meaning

Example : 2002, Anne McAllister, The Great Montana Cowboy Auction, Silhouette Books (2002), ISBN 9780373484577, page 22:  He was a notch on her bedpost, a stepping stone on her quest for stardom.2007, Melinda Curtis, Count on Love, Harlequin (2007), ISBN 9780373714483 , page 167:  She'd confused Sam's attentions with real feelings, and now she was just another notch on his bedpost.2010, Jenna Black, Glimmerglass, St. Martin's Press (2010), ISBN 9780312575939, page 138:  Bad enough to think he'd wanted me as just another notch on his bedpost, but to think he'd tried to seduce me for cold-blooded political purposes was unbearable.2011, Peter Robinson, Before the Poison, McClelland & Stewart (2011), ISBN 9780771076237, unnumbered page:  […] He wasn't a notch on her bedpost. They were in love, for crying out loud.'