hang out one's shingle, to

Open an office, especially a professional practice, as in Bill's renting that office and hanging out his shingle next month. This American colloquialism dates from the first half of the 1800s, when at first lawyers, and later also doctors and business concerns, used shingles for signboards.

To open an office, especially a professional practice. This term comes from nineteenth-century America, when lawyers, doctors, and various business concerns often used actual shingles for signboards. Van Wyck Brooks, in The World of Washington Irving (1944), wrote, “Catlin hung out his shingle as a portrait-painter.”