Acquiring by a popularly recognized method of transaction - Situmta
Note: As Rashi Bava Metzia 74a explains, "situmta" actually refers to a mark made by wine merchants on their barrels, to identify them as having been sold. However, Tosafot in Bava Metzia 66a "uManyumi" explains that this action represents a class of actions which are popularly recognized as methods of transaction, even though they are not identified as such in the Torah.
Validity of situmta: Bava Metzia 74a
Is situmta enough of a transaction that it is 100% binding, or is it only an indication of commitment serious enough to warrant a "mi shepara" if a party backs out afterward: Bava Metzia 74a