The following description was prepared by William Gross:
From earliest times, man has tried to protect himself from misfortune by the use of objects which he considered holy or otherwise (e.g., magically) potent. Amulets and talismans are items generally worn around the neck or wrist, carried in a pocket or purse or hung on a wall. They are meant to protect or aid those who carried or wore them. The Hebrew word for amulet, kame‘a, has the root meaning "to bind". Jewish amulets are usually comprised of texts (either letters or graphic symbols) that are inscribed on some sort of material; some may also contain plant matter or precious stones. The texts of amulets usually include holy names that are believed to have the ability to affect reality, along with incantations summoning angels or other magical powers. For the most part, an amulet has a specific purpose: to ease childbirth, facilitate recovery from illness, improve one’s livelihood, and so on, but in the modern world many are also made for general protection.
It was a custom in Germany to take a coin and to either inscribe or cut out the letter "Heh", creating an amulet. It has been postulated that this amulet, which was created for a male child, was connected with the protection of a child for whom the Pidyon Ha-ben ceremony could not be performed on time. Such amulets are found on American coins as well among those families who emigrated from Germany in the 19th century and early 20th centuries.