It was an informal affair. A seaman looking for work would go to the shipping office of a line that he thought might employ him. He presented a little book called a Continuous Certificate of Discharge, This showed all his work history, with each voyage signed off by his captain. It was traditional for a seaman's work and conduct to be rated "Very Good" unless he was quite useless, in which case the captain "declined to report" andn his career was finished. The line engaged men as required. Sometimes the unions helped assemble a big crew, as on Titanic.