I am using Anki 2.1.44.
Beginning a search term with a hyphen matches cards not including the search term. To search for a term beginning with a hyphen, it used to be possible to escape the hyphen with a backslash, or to use quotes, as explained in the documentation.
However, this no longer works. Entering a search term beginning with -, the search term is automatically changed to begin with -. Similarly, quotes are automatically removed.
Escaping other characters (e.g. : \ *) seems to still work fine.