How do I Customize the boot screen for Mac OS 7?

I recently dug out my first computer (a Macintosh SE) from storage. My mother bought it from her boss back when I was 13, and at the time it would boot with her old company's logo (instead of the traditional "Welcome to Macintosh"). Since then, the computer has been wiped, and restored. When that happened, the custom boot screen was lost. I was wondering if anyone knew how the "original" custom screen was achieved? I'm not saying that I want my mother's old work logo back, but I would love to put a personal touch onto one of my favorite macs.