On receiving their office assignments, new senators publicize their postal and email addresses to encourage communication with constituents. Long before email guaranteed citizens instantaneous access to their representatives in Washington, Senator Harry Truman jokingly informed his Missouri constituents that they could easily reach him at the following simple address: "Truman, S.O.B., Washington." Even as an obscure first-year senator in 1935, Truman knew the post office would direct any envelope marked S.O.B. to a member of the United States Senate.
That abbreviation for "Senate Office Building" served nicely until 1958, when a second facility opened. After that, senators had to specify in their addresses whether they resided in the "Old S.O.B." or "New S.O.B." Fourteen years later, in October 1972, the Senate provided for a third structure. This would eventually require each building to have a distinctive name. The old and new buildings, designated to honor two recently deceased Senate leaders, became the Richard Russell and Everett Dirksen Buildings, respectively. In 1976, shortly after ground-breaking for the third building, the Senate named it for Michigan's then terminally ill senior senator, the widely admired Philip Hart.
The practice of honoring particularly distinguished members on the Senate side of Capitol Hill had begun two decades earlier, in 1955, with the naming of a new bell tower for the late Republican Majority Leader Robert Taft. That same year, the Senate set up a committee, chaired by Massachusetts Senator John F. Kennedy, to select five outstanding former members, whose portraits would be permanently displayed in the Senate Reception Room. In 1964, the Senate provided for the placement of plaques in adjacent Capitol rooms assigned to the two senators who formed the 1960 Democratic presidential ticket–John F. Kennedy and Lyndon B. Johnson. Since then, other Capitol spaces have acquired designations associated with former Senate leaders. They include Arthur Vandenberg, Styles Bridges, Hugh Scott, Mike Mansfield, Robert C. Byrd, Strom Thurmond, Howard Baker, and Bob Dole. In 1998, plaques were installed in the original "S.O.B." to mark rooms once assigned to senators who subsequently became presidents of the United States: Warren Harding, Richard Nixon, John Kennedy, Lyndon Johnson–and Harry S. Truman.
Baker, Richard A. The New Members' Guide to Traditions of the United States Senate. (Washington, GPO, 2006. S.Pub. 109-25), 20.