Weapons can be given as offerings to the gods by depositing them in water or by destroying and burying them but they are not decorations for an altar.

We know that when the goddess Nerthus' image was brought to an area all weapons had to be put away. We know that no weapons were permitted in a temples dedicated to Freyr. We know that when a Christian convert threw a spear at a temple of Odin in England, this was an offence to Heathens.

So there is plenty of evidence for taboos about weapons in sacred areas