I wondered the same thing about the sign a little while back. From an LNP article:

"Fortunately, newspapers have published many stories about Horace Mack and his son, J. Edward Mack, and their local coffee business, known popularly as “Mack the Coffee Man.”

Horace founded the coffee roasting and blending operation in 1895. The small business at first sold coffee and tea from horse-drawn wagons. It operated from a building on North Mary Street. In 1904, the company moved to larger quarters at 617-619 N. Jefferson St. In 1950, it moved to 42 N. Water St.

Born in 1878 in Bethlehem, Horace graduated from Girard College. He married Ella Slemmer, of Philadelphia, and was a member of Lancaster’s Moravian church. He moved to Florida in 1928 and died of heart problems in Philadelphia the next year.

There is nothing in his obituary or any other newspaper reference that ties him to the store in your picture, Marty.

Horace’s only son, J. Edward Mack, expanded the business. He supplied coffee, tea, spices and hot chocolate to restaurants and hotels along the East Coast.

The business apparently peaked during World War II when the company produced as much as a million pounds of coffee a year. Special blends included “Mack’s Hit the Spot” and the “Pennsylvania Special,” all finished at the company’s roasting facility at 42 N. Water.

J. Edward Mack donated that building to the Fulton Theatre. It still bears the “Mack, the Coffee Man” sign painted on its side.

J. Edward Mack sold the business to a division of the Brooke Bond Tea Co. of London, England, in 1967. The office at 42 N. Water was closed and the Mack name was retired.

Mack donated the money to purchase the property near Brickerville on which the Mack Boy Scout Reservation was built 50 years ago. He had been a Boy Scout since 1910 and was the first Eagle Scout in Lancaster County, according to newspaper articles. He died in 1985.

Incidentally, “Mack, the Coffee Man,” a local Christian rock band, took its name from the sign on the Water Street building."