"There's rosemary, that's for remembrance." (Hamlet, iv. 5.)
In the Middle Ages, rosemary was associated with wedding ceremonies. The bride would wear a rosemary headpiece and the groom and wedding guests would all wear a sprig of rosemary.
As well as being linked to remembrance, rosemary was also used to symbolize love and loyalty.
In Australia, sprigs of rosemary are worn on ANZAC Day and sometimes Remembrance Day to signify remembrance.
As a side note: It's also one of my favorite cooking herbs. :)