Well, first make sure all your images (minus the MAL sig image) are uploaded to a free hosting site, like Photobucket or Imageshack.
Next, you go to Edit Profile > Forum Settings
As Stench said, if you quote his post you'll be able to see what his codes look like. But I'll put them here, anyway, using curly braces instead of square brackets so you can see them.
{url=http://myanimelist.net/animelist/solid-snake&sclick=1}{img}image1url{/img}
{img}MALsigurl{/img}{img}image2url{/img}
{img}image3url{/img}{/url}
Of course, you may need to rearrange them, especially the second row, depending on where in your banner the MAL sig is placed (left, right, or middle).
If you want it centered, put {center} above and {/center} below the images.
Just remember to use the square brackets! :)