Rubenstein senior VP Laura Hynes-Keller and senior executive VP Marcia Horowitz are handling Siebert, a long-time agency client.
Siebert was the first woman to own a seat on the New York Stock Exchange and first to head a member firm. She also was Superintendent of Banking for New York State for five years and an innovator in the discount brokerage field in the mid-1970s.
She founded and led SFC until her death in New York on Saturday from complications from cancer.
Joseph Ramos, COO and principal executive officer of the brokerage, will continue a role similar to Seibert, the company said.
"Although she is best known as the first woman to own a seat on the NYSE, she really became one of the great personalities on Wall Street of either sex," Ramos said in a statement. "We will work to continue her legacy."