hang out/up your shingle
hang out your shinglebegin to practise a profession. North American
The main and oldest sense of shingle is ‘a wooden roofing tile’, but in the early 19th century the word developed the more general sense of ‘a piece of board’, while in the USA it also acquired the particular meaning ‘a small signboard’. Literally, hanging out your shingle refers to hanging up a sign that advertises your profession.