I had to find a manual for my washing machine to disable the child lock which accidentally got turned on. There's no symbol (maybe kids are onto that these days), you just have to intuit which buttons you have to hold at the same time.

Plus points: you can turn the beep volume down.

Minus points: without a manual you would never in a million years figure out the magic sequence to get into the menu and when you did what the numeric menu codes mean.