There is an episode in the Liber Historiae Francorum, an anonymous work detailing the quasi-mythic history of the Franks dated to the year 727, which mentions king Clovis choosing a place to build a church dedicated to the Apostle Paul.
His queen Chlothild had suggested to the king that if he built such a church he would surely have victory over the Goths. Upon hearing this suggestion, Clovis thought that it was good. He then took out his francisca, a Frankish war ax, put it before him and threw it. He then said, according to the source: “Let the church of the blessed apostle be built there when, with God’s help, we return”.
This episode is a short one but I think it holds an important piece of the puzzle when looking to reconstruct Frankish sido. Although the information being relayed is written nearly three hundred years after the reign of Clovis, what we are reading may be a custom that had remained ingrained in the mind of the author as one that was either common enough to the Franks or something he heard that the Franks did in the distant past.
Assuming this is what took place and that Clovis did use his ax to, with the help of God, establish a church, it has some interesting cognates in Scandinavian sources. One which comes readily to mind is the use of Öndvegissúlur (high seat pillars) during the settlement of Iceland, to locate the favorable location of a future homestead. The early Icelanders took carved pillars that where emblematic of the gods and threw them overboard, into the sea. Wherever the pillars landed, that’s where their homestead would be erected.
However, in the case of Clovis, what he uses as his aid in revealing the will of God (maybe the gods in pre-conversion times) is an ax. Specifically this is a war-ax, which was one of the primary martial weapons that the Franks used in combat and widely referenced in sources. This then seems similar to another Scandinavian war custom, though at this time the source escapes me, where one would throw a spear over the enemy to ensure victory.
If we break the episode down, what we seem to get is Clovis agreeing that a new holy place should be established to give him luck in battle and that in using his francisca, God (or gods) is able to establish the location and in a sense is made holy. Since the Franks were a martial people, it makes sense that they would use a war-ax as an instrument of the will of the gods in dedicating a holy site.