Bank note refers to the Quality of Life feature which is not found on authentic RSC, allowing any item to become a stack. The majority of items have a "noted" counterpart, which allows an unlimited number to be held in 1 space inside the players inventory. The player has the option to withdraw items from the bank in this noted form, and depositing them will return them to their original state. This feature was implemented to the original ORSC server and Cabbage in order to allow for easier trading of items between players. On Cabbage, it is also helpful for players who wish to put items for sale in the Auction House, as well as making selling large amounts of items to NPC shops easier. Some items cannot be noted, such as untradeable items and quest items.
This function does not remove the certificate system found in authentic RSC, and the certer NPC's are still available. However, these NPC's now have a dialogue option which will 'uncert all to bank'.
If a player finds an item which they cannot note, but feel it should be allowed, please submit an issue on the Gitlab page found here.