A sign which is used to join one letter with another is called Sakin. For example see below word, blue sakin joining red qauf with black letter ‘daal’ making joint pronunciation ‘Qaud’.
Sakin also could look different in various fonts like Nurani, Uthmani, Saudi Arabian type etc. See below image for most used sakin faces. pp
More examples of how sakin joining one letter with another see below.
Now see below how it looks in Quran.
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