I found this site on the internet, which personalizes the actual state license plate. I made one for each student, then copied the picture into Word and made it bigger. The pictures are a little bit blurry, but not too bad, especially since no one will be looking at it close up.
I'm pretty well versed in using Adobe Illustrator and Photoshop, so making signs etc. is pretty easy for me. So, to answer your question about how hard it is to make a sign like that, I would say it would be very difficult for someone without a graphics background. As I've told others, making things like this is kind of a hobby/stress reliever for me. I enjoy doing it alot. If there's something you need made, don't hesitate to contact me and ask. Sometimes when people give me an idea for something, I end up printing one for myself.
I teach in California and I am also using this theme as my back to school theme. I might use "On the road to success" or "Driving into a new year" as my slogan. I made my own license plate template to use. It is pretty easy. I just made it in word. Now I just need my class list!