This had lead to some confusion when end-users attempt to order additional cash drawer inserts. One of the best ways to tell is located on the front left of the front of the cash drawer. You will see a large sticker that is a 56 or a 57 and then you know what type you have. Often that sticker has been removed so again you don't know.
The second way to identify the insert type is the insert itself. The original drawer model 56 has a two piece insert. The coin tray of the 56 will remove from the rest of the insert. The 57 insert is a one piece and the coin tray portion itself does not separate from the insert.
Below I have added some pictures with labels to help you identify which you have. Here is a link to where you can buy either insert for the SAM4s SPS-520R cash register.
Type 56 drawer (see label front left)
Type 57 drawer (see label front left)
Type 57 Insert