If the brand of an item is unknown then there are two options  -

  1. The Brand field is empty.
  2. The Brand field shows as Unknown Maker

Use the former if the item is an unbranded item where it is unlikely that the Brand will ever be known and the latter if the item has been made by a Brand but it is hard to identify which one (for example the packing is missing or the writing is weathered).

This BMW 504 model is a good example of a good use for Unknown Maker (the hope is that one of the other users knows the item's Brand and will be able to add it)  -

Unknown Maker is not for other fields than Brand.  So if say Hot Wheels created a fantasy model it does not need to be added to Unknown Maker.