I was wondering if someone might ask that question.
Every one of these strange sketches is a SketchUp drawing with a style I created. I made the style by combining several image file elements. The sketchy lines are image files --some of those line styles you would already have on your computer.
Lets take the Etch-a-Sketch image as an example. I found the image of the Etxh-a-Sketch through a Google image search. This was saved to my computer. The saved image was imported as a Watermark background as well as an overlay. This is done under the Edit tab of the Styles dialog.
I also made a PNG file of the Etch-a-Sketch in which the screen area was deleted. This was done in a freeware image editng application called Paint.NET but you could use most any editor for this. Saving it as a PNG allows the deleted area to display as transparent. This image was brought in as an overlay with the transparency slider set all the way to Image. The frame of the Etch-a-Sketch becomes a mask and covers the drawing if the drawing extends behind it.
So if you were to look at the images as a stack with the front on top you would have the following
Image.png (transparency slider all the way toward Image)
Image.jpg (transparency slider closer to Model. this adds a little bit of texture over the model)
Model
Image.jpg (transparency slider all the way to Image since it is the background.
The line style is selected from the Sketchy Lines and draged to Edge Style under the Mix tab.
I also adjusted the background color so it was close to the color of the screen and set the face display style to Hidden Line. Hidden Line keeps faces from showing as different shades of the face color. The face color though comes from the background color.
After all the settings are made, type the name of the style in the name box at the top. Add a description of it if you like in the larger box. Then click the Create New Style button along the right side of the dialog box.
Finally, to save the style so you can use it on other models, open the secondary Style window. Click on Select and choose In Model for the Primary window. Select your destination folder for the secondary window and then click and drag the new style from the Primary to the Secondary window.
If you want, you can make new style folders. There are a couple of ways. The easiest to explain is to use Windows Explorer to navigate to the Styles folder under Google SketchUp 6 and make a new folder there. The other way is to click on the Menu button in the Styles dialog box and go through the steps to Create a new folder.
Now, last but not least, like materials and components, unused styles stay in the file for your model unless you purge them. You can either click on the Menu button in the Style dialog and choose Purge Unused or you can use the PurgeAll plugin or you can open Model Info>Statistics and click on Purge Unused there.
CLear as mud?