"on the faucet"
This symbol is unnecessary. It's just as normal as ا.
I hope though that Duolingo is not giving users hard time with this one like they did (and still do maybe) with the dagger-Alif in هذا.
The symbol on Alif here is mostly seen in Quran orthography, and calligraphic arts, and it has to do with how the Alif is to be treated when reading it (it's just the opposite of Hamza أ).
and by the way, the symbol is a small صـ - but as i said, it's not important
This said, not every expression in English using any of these preposition would match exactly the Arabic version. And this is not only the case with English and Arabic but also between English and other European languages. For example, you might say in the morning in English but in Irish you might say ar maidin which literally means (on morning).
So, while the above are direct translations for "on" and "in" into Arabic, but don't expect their function and usage in Arabic to match that of English.