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Yesterday when I was solving some basic geometry problems, I was curious ( I'm still though! ) about something:

Why / When do some people indicate the angle with its measure $= 90^\circ$ by adding a point inside it?

I like history, too, so if it's possible I want to find the story behind this notation.

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    I've never seen this style of right-angle indicator (with the dot). Do you think it's more common in some countries than others? – 2017-02-24
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    @Joffan My fault then, but in my zone ( Romania ) it is used. But it is also used the notation without the point, too... – 2017-02-24
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    No fault involved, interesting variation. – 2017-02-24
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    @Joffan Now, I don't know what to do: to delete the question or let it be? – 2017-02-24
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    Definitely let it be, maybe someone will have another insight. – 2017-02-24

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According to Wikipedia:

In diagrams, the fact that an angle is a right angle is usually expressed by adding a small right angle that forms a square with the angle in the diagram, as seen in the diagram of a right triangle (in British English, a right-angled triangle) to the right. The symbol for a measured angle, an arc, with a dot, is used in some European countries, including German-speaking countries and Poland, as an alternative symbol for a right angle.

Note that it talks about an arc with a dot, not a square. For what it's worth, I've seen both "little square with dot" and "little square without dot" in Greece. I've never seen an "arc with dot".

I will be quite surprised if there is any particular story behind this notation. It is probably a matter of different communities using different notation for the same thing. Another example of this phenomenon concerns, e.g., the Notation for intervals.

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    I am from Austria, Wikipedia states correctly, we use (to the best of my knowledge) the arc with the dot to signify the right angle. – 2017-02-24