The switch symbol dates back to the very first international Lisa keyboards from 1983. They needed a language-independent symbol for the "Option" key in 1983,

The switch symbol dates back to the very first international Lisa keyboards from 1983. They needed a language-independent symbol for the "Option" key in 1983, that's what someone chose, and it stuck. Some other keyboard trivia: - The 1983 Lisa used the Apple logo for its command key. The 1984 Mac used the cloverleaf symbol instead because Steve Jobs didn't like seeing so many Apple Logos in the main menus. - The command key has been around since 1983, but is was never labelled "Command" on the US-English keyboard, nor was that key referred to as "Command" in the documentation. It just lore that this strange cloverleaf key was called "Command", and passed down through oral tradition. Apple finally labelled the key in the late 2000s. - Apple has been very conservative about its keyboard layouts and symbols. The original Mac and Lisa had separate Enter and Return keys. The separate "Enter" key survived will into the 2000s iBook and Powerbook keyboards. It was finally removed with the MacBook in 2006. - Likewise, the Apple Logo was added to the command key in 1986, for compatibility with the Apple II. It wasn't removed until the late 2000s. - The Apple Extended Keyboard from 1987 was Apple's first keyboard to use a PC-style 104 key layout. This keyboard includes all of the PC-specific text such as Alt, Scroll Lock, Print Screen, etc. This is how the Option key came to be knows as "Alt" on non-US keyboards.