Click on Edit
Select Message Filters
Click on New
In the Filter Name box type Spam, below this box select "Match any of the following".
In the first drop down box select subject, in the second box select contains, in the third box type *****SPAM*****.
In the next drop down box select Move to folder and in the following box select Trash.
Then click Ok on the bottom of this box and Ok on the bottom of the next box