The Viking cross (a symbol in the form of a “plus” sign with “serifs” at the ends) was a Viking religious symbol that came from the Latin cross (the Romans, who in turn got it from the Greeks). Long before Christianity, pagan peoples were using crosses as religious symbols, most often representing the sun, or the earth (the four corners). In addition to these meanings (the Vikings held the sun in high religious regard according to many sources), the Viking cross and its related symbols (such as the swastika) represented war itself due to the fact that these types of symbols represented Thor--the lines with “serifs” at the end representing his hammer (Bruce-Mitford, 2008).

An example in architecture would be the Viking ring fortress. All the fortresses had a circular rampart built of earth and turf. This rampart had four gates placed at equidistance from each other (at all four-points of the compass). Covered structures called “gateways” were built around these gates and were probably crowned with towers. Linking the gates internally, were two timber-paved streets, one running north-south, the other east-west (Roesdahl, 1987). The two streets form a cross shape (“plus” sign) and the gateways at all four ends of them (where the attackers “base camps” would be in Tablut) make for a comparable design to the Viking cross.

By the time Vikings were printing coins (later-half of ninth century), Christianity was beginning to take hold among the Danish Vikings (Christianity did not take hold in Norway for another two centuries). However, belief in the norse gods did not die out overnight and Viking beliefs and Christian beliefs were melded together for a time. “Many Christian Vikings kept their faith in Thor, just in case.” (Margeson, 2010).

One example is when the Vikings printed coins. The coins depict the names of Christian kings of East Anglia who were defeated and killed by Vikings in the early ninth century. “All of these coin designs give a fascinating insight into the way in which Scandinavian political dominance was maintained and made palatable through recognizing and respecting the traditions and susceptibilities of the Anglo-Saxon population. Indeed, the coins may represent deliberate attempts to create regional power blocks in which the children of Viking invaders and the children of the conquered Anglo-Saxons were bound together into carefully manufactured and unique identities.” (Hall, 2007).

Take a look and see if you recognize anything:
http://www.dorchesters.com/shop/viking/vikings_york_st_peter_coinage.htm
https://www.yorkcoins.com/jca1__-_kingdom_of_east_anglia,_eadmund_(855-870),_silver_penny.htm
http://www.stedmundsbury.gov.uk/sebc/visit/865-1066.cfm
(scroll down to the coins)

http://www.yorkcoins.com/me308_%E2%80%93_sweden,_olof_sk%C3%B6tkonung_(994-1021_1022),_penny,_2_09g_,_sigtuna_mint.htm

Sources:
Bruce-Mitford, Miranda. Signs and Symbols. DK Publishing. 2008.
Roesdahl, Else. The Vikings. Penguin Press. 1987. Page 136.
Margeson, Susan M. Eyewitness Viking. DK Publishing. 2010. Page 63.
Hall, Richard. The World of the Vikings. Thames & Hudson, 2007. Pages 108-109.