U.S.B.R - United States Bureau of Internal Revenue is a solid brass padlock.
The U.S.B.R. is a tamper proof paper seal padlock. A U.S. Patent was issued to Thomas Slight on August 5, 1878 and produced by Slaymaker Lock Co. in Lancaster, PA until the early 1920's.
Tech Info -
The key rotates counter clockwise to unlock and a window reveals a paper seal.