One indicator for passion for coding I've found reliable is whether the job candidate has written anything for themselves - not for money, not for homework, but just writing a program to address a problem or goal they identified for themselves. It's often very telling how a candidate talks about such projects - do they become animated / excited / enthusiastic to tell you about their little creation? Did the project evolve over time (most do)? When did they find time to work on this project? How sophisticated did the solution become? And most importantly, what did they learn from doing this project? What would they do differently?
For example: a high school student that wrote their own livestock pedigree tracking program. Did it use a database or home-grown storage (why/what tradeoffs/lessons learned)? Bonus points for figuring out how to generate and print a 4 generation pedigree printout. Etc.
Another example: Writing a program to compute and display fractal images is ok. Supporting user interaction to navigate through fractal space (click to zoom, click to render related fractals (Mandelbrot vs Julia)) is better. Distributing the fractal computation across multiple networked computers using basic TCP/IP: outstanding.
It doesn't really matter what the project is about. It simply provides a platform for conversation, so that the employer can get some insight into how the candidate thinks and feels, what motivates them, and how they make decisions.