DALLAS — On the morning of Nov. 22, 1963, Lee Harvey Oswald left his wedding ring in a cup on the dresser and left $170 in one of its drawers before he headed to work at the Texas School Book Depository.The gold band that belonged to the man who assassinated President John F. Kennedy that day is among nearly 300 items linked to the former president that will go up for auction today in Boston. Bobby Livingston, an executive vice president with the New Hampshire-based auction house RR Auction, described the ring, which has a tiny hammer and sickle engraved on the inside of the band, as a “very powerful, significant piece of evidence.” “It gives you such insight into the mind of Lee Harvey Oswald,” said Livingston, who added that it could bring $100,000 or more. It was only recently that the seller, Oswald’s widow, Marina Oswald Porter, recovered the ring, which apparently sat forgotten for decades in the files of a Fort Worth lawyer who once worked for her. With the 50th anniversary of Kennedy’s assassination in downtown Dallas approaching, the auction house has gathered items ranging from Kennedy’s rosary beads and clothing to Oswald’s Marine Corps rifle score book to a hat worn by Jack Ruby, the nightclub owner who killed Oswald two days after the assassination. Accompanying the ring is a five-page handwritten letter, dated May 5, 2013, in which Porter writes: “At this time of my life I don’t wish to have Lee’s ring in my possession because symbolically I want to let go of my past that is connecting with Nov. 22, 1963.” At her request, the auction house is not releasing the full contents of the letter, in which Porter documents the history of the ring, from its purchase in the Soviet city of Minsk, Belarus, before their April, 30, 1961, wedding, to how it was left on the dresser at her friend Ruth Paine’s home, where she and their children lived when Kennedy was killed. Oswald, who lived during the week in a rooming house near downtown Dallas, usually visited only on the weekend.The ring took a circuitous route from the dresser to the auction. In 2004, it was found in the Fort Worth lawyer’s files. It was in an envelope marked “Treasury Department Secret Service” with a receipt stating that Paine gave it to the Secret Service on Dec. 2, 1963. A July 2012 letter from the Fort Worth law firm of Brackett & Ellis to Porter says the ring had apparently been in lawyer Forrest Markward’s possession since 1964. Luke Ellis, a partner at the firm, said that when the ring was discovered, the retired Markward couldn’t recall exactly how it came into his possession. Markward has since died. Also up for auction today are a white Lincoln Continental that the president and first lady rode in hours before his death and the sixth-floor window believed to have served as Oswald’s sniper perch, which the building’s owner removed in the weeks after the attack.