Q. I signed a contract forming a partnership, but made no additional kinyan. Is the partnership binding?
A: Shulchan Aruch rules that for a partnership agreement to be binding, it must be consummated with an appropriate kinyan, or that the parties begin implementing the partnership (C.M. 176:1-3; Nesivos 176:3).
However, Chasam Sofer (C.M. #96) writes that if there is a common commercial practice, the minhag hamedinah is binding. For example, the practice of his time was that when people hired a wagon together to travel to the market, any profit that one earned along the way was shared jointly. Even if no additional kinyan was made, they were not partners beforehand and did not explicitly stipulate this, they are considered partners on account of the minhag hamedinah (Pis’chei Teshuvah 176:3; Pis’chei Choshen, Shutafin 1:14)
Similarly, many poskim consider signing a contract nowadays as binding on account of minhag hamedinah, so that your partnership agreement is binding, despite the lack of an additional kinyan.
