On page 74 of the User Guide for the Canon S50 in the
section titled "Selecting an AF Frame" step 1 states

Press (and then there is a box with 3 dots in it.
Under that it states "The AF frame appears in green on the LCD monitor."

I can't find any button, switch, etc with three dots on it.

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Where is the | . . . | Button?
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Best I can do.