This exists because customers asked for it, not because it is a traditional object — five-coin charms are normally kept in a wallet, a purse or hung by a door, and the car version is a modern adaptation. We flag that because it is easy to assume every object on a site like this has a long history behind it, and this one does not.
The coins are cast brass reproductions, as with our other five-coin pieces. The tassel is polyester rather than silk, because a car interior is a hard environment — sunlight, temperature swings and dust — and silk would fade and shred within a summer.
On positioning: hang it where it does not sit in your line of sight. Several US states treat an obstructed windshield as a moving violation, and in any case the point of a mirror is to see out of it.