CREATE OR REPLACE FUNCTION TestFunc(p_year IN VARCHAR2, p_sign IN NUMBER)
  RETURN NUMBER IS
  RESULT     NUMBER;

...

using (OracleCommand command = connection.CreateCommand())
{
 command.CommandText = "TestFunc";
 command.CommandType = CommandType.StoredProcedure;

 command.Parameters.Add("p_sign", unit);
 command.Parameters.Add("p_year",year);

 var result = new OracleParameter("RESULT", OracleDbType.Int32, int.MaxValue) { Direction = ParameterDirection.ReturnValue };
 command.Parameters.Add(result);
 command.ExecuteNonQuery();
}

command.BindByName = true;