The term Muslim Cross begs qualification. It is a cross used by some Muslims but does not represent Islam nor the Crucifixion of Jesus2. It is one of several different geometric cross patterns used by the Sunni Muslim3 Tuareg people of Saharan Africa.
The centre of the cross represents God and since Muslims believe we are one with God, mankind shares that central spot. The four arms of the cross are to keep evil at bay and this cross is worn as a protective amulet. Muslims also believe, of course, that a few grams of shaped metal cannot protect anyone from evil (see Charms); only the love of God can do that. Nevertheless, like prayer beads used in many other religions, this cross is a symbol of one's faith.
The Tuareg are Berber nomads and most now live in west Africa, principally Niger, Mali, Algeria, Burkino Faso and Libya. Given their nomadic traditions, the four arms can also be seen as conduits for spreading love to the four corners of the world, similar to the Christian's Mission Cross.
Generally shunning anything that could become idolatrous, Islam doesn't have many symbols (the Crescent being an obvious exception) consequently Muslims have copied artwork from Christianity4 giving it their own meaning, just as Christians copied pagan artwork.
Whilst the Tuareg Cross is not supposed to represent Christianity (nor Islam) it is probably based on the Christian cross. Before the arrival of Islam, Berbers were Christian and very familiar with Christian art. As with the Coptic Cross, the circle at the top of this cross is most likely inherited from the Ankh, where it originally depicted the Sun god.