And got it to work from XAML. Now I'm moving all that to code-behind. I've got the tiled map layer showing up, but can't get the graphic. Stepping through the code, I can see the Symbol loading properly and I'm definitely using the same coordinate as I set in the XAML but nothing shows up.
vehicle = new Graphic() { Geometry = new MapPoint(-122.123889, 47.669444), Symbol = LayoutRoot.FindResource("RedMarkerSymbol") as Symbol };
GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphicsLayer"] as GraphicsLayer; graphicsLayer.Graphics.Add(vehicle);