At the Northwest Aviation Conference we spoke to a Seattle Tower controller who described for us in easy to remember pilot terms the new VFR transition names on the Seattle VFR Terminal chart: Seahawk and Mariner.
The two transitions fly over the north numbers and over the south numbers. The first step is to determine the traffic flow - where is Seatac traffic landing from, is it north flow or south flow.
For your VFR transition you will want to fly over the numbers where the traffic is LANDING. That will determine which TRANSITION to use.
The controller said it's easy to remember which transition is which - they are named in the order of the stadiums from north to south - Seahawk and Mariner! Doesn't this make sense?
When you get close, listen up to Seattle tower, get close to your entry point at the required altitude, then make the radio call with your location, altitude and type of transition you want. The tower, she said, must confirm your altimeter setting and your altitude after you get a squawk code even if you gave your altitude to them already.
She said the tower has no problem with VFR transitions but to just be a little patient if they are super busy.