If you think this pendant looks like the Hammer of Thor, you would at least be geographically very close since this cross was seen in Trondheim, the ancient Viking capital of Norway. However, an element that doesn't correspond in any way to Thor is the pendant's inlay of abalone shell (mother of pearl).
As a cross, it is unusual. The seashell's maritime association, plus the unusual orientation and overall shape, leads us to think of an anchor. The D-shaped arm ends resemble mushroom caps or axe blades, but it's more likely the curves are supposed to substitute the circle around a Celtic Cross, meaning eternity.
On the topic of mushroom caps, the hallucinogenic properties of some mushrooms (psilocybin) have historically been used as a mystical path to the spirit world, at least in the minds of those taking the trip.
The real mystery is not whether people actually can get closer to the spirit world, but the question is: Why do people feel that such drugs are important to do so? God designed humans in a way that they communicate with Him quite easily, without drugs. For most people who talk with God, having a clear head, free from any mind-altering 'shrooms', is important.
Yes, many religious people get a 'high' listening to choir music, a rousing sermon, or breathtaking scenery. And proponents of using 'sacred' mushrooms could argue that the hallucinogen is made by God. That is true, and it is up to each of us to decide whether God made it as a spiritual aid, or as an anesthetic for pulling teeth.
And in excluding the likelihood of the semirounds representing axe heads, we note that Norwegian art from the Viking and High Middle Ages usually depicts axe heads with concave edges, as seen in the coat of arms of the Church of Norway. This is based on the 16th century archbishops of Nidaros coat of arms, showing a Budded Cross with two axes in honour of the martyrdom of King Olav II, killed in the Battle of Stiklestad on 29 July 1030.
The sea shells represent baptism (as described for the Compostelan Cross). The predominant faith in Norway is Lutheranism and in that tradition, baptism is a sacrament that gives eternal salvation. The shell representation of baptism complements the rounded arm ends that represent eternity.
The Norwegian Rite was predominant in the Channel Islands of Britain for a time.
On baptism: Titus 3