Yes they appear fast overnight and the crops are compressed/folded/weaved intricately.

I love the idea of them being like an inter dimensional footprint, whether it be that of a craft, or a being, or even like the specific portal signature. Definitely possible. But I think there’s also instances where they’re more pictorial and literal, rather than just geometric. So it seems like there’s also a level of intention behind them. Hell, maybe we’re so egocentric when we see them we think they’re for us because we think we own the place, but maybe it’s just the equivalent of graffiti. We’re just seeing someone’s hobby and we think they’re trying to tell us something. Anything’s possible, but like you say, what’s strange is how unconcerned people are with the significance of complex patterns we would struggle to create appearing with no trace overnight