Note: A sword signature,  codified by tradition in the Shinto period, has several normal elements. First may be the Province of residence of the smith. Second may be a title, if he is a titled smith. see Titles

"Fujiwara" aand "Minamoto" are the ancient and revered families of Japan and these were used in sword signatures often as reference to cultural affiliation. Minamoto refers to Samurai, Fujiwara refers to Nobility and by extension, to the Emperor.
There are ancient leanings in Japan, either to the government of the Samurai, the Minamoto being the first, or to the Emperor. The Samurai have been thought of as having usurped power from the Emperor - and there has been a long history of tension between the these two. It is more than mere governance - it holds the basis of Japanese culture and even to religious feeling.

In sword signatures, the terms, "Fujiwara" and "Minamoto" are mostly a begnin aspect of signature - however, some swords show, through the styling or mountings, a more ardent affiliation. There have been several attempts through Japanese history at Imperial Restoration - and the passions have always run high. Occasionally we see some swords having been made for a particularly passionate individual.