They lived on an island in the middle of a vast sea. When ships approached, they'd sing beautiful songs to lure sailors to their island.
Sirens represent mystery, enticement, beckoning.
Remember, your web site should mirror you or your organization in some way. If you owned a grocery store, you wouldn't want customers to see it overrun with dirt and grime and roaches. You wouldn't want them to see sloppy, disorganized shelves. And you definitely wouldn't want to send them spinning on their heels in a mad dash for the door just seconds after their arrival.