Sceptical that this means that there were Muslim Vikings. Arabic script was commonly used throughout medieval Iberia as decoration, often without any meaningful words, just Arabic letters strung together for aesthetic effect. Wouldn’t surprise me if something similar was going on here, where Iranian weavers were simply mass producing cloth for export with Ali and Allah embroidered as decoration. Keep in mind that Vik…
Here in Lithuania (well the empire, so Poland and Belarus too) there were a large number of Muslim settlers who arrived in the 14th century. They were known for their military strength and were invited by Vytautas to aid in the efforts against the Christian Crusaders. If military prowess was as highly regarded as we believe to the Vikings, I wouldn’t be surprised if they did something similar too.
While we're at it, one of the founding myths about Christianization of Kievan Rus involves knyaz Vladimir holding a council on which faith to convert to, and inviting preachers to compete - supposedly, Latin and Greek rites of Christianity, Islam (via Volga Bulgars), and Judaism (via Khazars) were all on the table. According to the legend, Islam was rejected first, solely on account of banning alcohol. Judaism was reviewed and rejected next, because the loss of Jerusalem and destruction of the Temple was seen as a clear sign of divine weakness by the pagan Rus. Finally, between the Greek and the Latin rites of Christianity, they picked Greek, because Greek churches and priests were decorated much more lavishly (with lots of prominently displayed gold etc), while Latin ones were more subdued.
While it's almost certainly a legend that does not correspond to an actual event, its very premise speaks volumes about how religion was viewed in that time period.