The Symbol of Thors Hammer (also known as the Mjolnir in Norse stories) has always been seen as a symbol of strength and protection. This comes from the early Pagan Norsemen who wore the Hammer as an amulet of protection long after Christianity had moved into their world, and it is still worn today, both by Asatruar and others of Norse heritage.
Mjolnir was a handy tool to have around, because it always returned to whomever had thrown it. Interestingly, in some legends Mjolnir is portrayed not as a hammer, but as an axe or club (also seen in Avengers: Infinity war)
In areas of Sweden, Denmark, and Norway, small wearable versions of this symbol have been unearthed in graves and burial cairns. Interestingly, the shape of the hammer seems to vary a bit by region. In Sweden and Norway, Mjolnir is portrayed as rather T-shaped. Its Icelandic counterpart is more like a cross, and examples found in Finland have a long, curved design across the bottom brace of the hammer.