We need brand recognition
As the number of manufacturers including Sirius XM in their products increase, Sirius needs a way to let consumers know that their product is involved. Consumers looking for the product will appreciate the ease by which they can quickly identify that Sirius is paired with this device.
Think of this as the "Intel Inside" advertising model. I can look at my laptop and tell that it has an Intel chip and MS Vista. When shopping for it, I didn't have to look too hard to determine which computer I wanted. Sirius can include a logo decal for each device that contains Sirius. When you look at the product, you can determine within seconds that it either does or does not have Sirius.
For larger ticket items, like cars, trucks, or SUVs (I know, but gas prices are coming down), you could put a decal on the window if it is a standard feature. This helps a car buyer identify a feature on the car. Anything that can sell a car is a plus in this tough market. Commercials could show a little icon in the corner.
Product branding is important, especially when other manufacturers are creating their own devices. Anything that helps the consumer buy Sirius can make the sale much easier. You wouldn't want the consumer to get confused and accidentally buy some crappy HD Radio.