Could you give me a source for this?

Preferably a Finnish one. Not by language (although am Finnish so not an issue) but like a reliable source in Finland documenting that’s what they’re for?

I know we do have lots of infra designed “in case of Russian attack”, mainly the direction of roads on the eastern border, but I’d like to read up on this blowing bridges shit.

I mean its also very much usable for other stuff like hanging up temporary cables and hoses and in practice its probably used for things like that more often.

I genuinely just think it’s the construction crew just bending the rebar that they had as extra when building it, instead of spending time cutting these off to make it look nice.

As in they needed like x meters of rebar so they used x +0.5m to make sure there is enough, and in the end just couldn’t be arsed to cutt off the extra, sand it down, paint over it, etc.

Cutting rebar is much easier than bending it, especially upwards and in a proper curve.
Also, those hooks immensely complicate the concrete framework. (If they were done during the initial pour)
So it’s pretty unlikely that they are leftovers from construction.
Cold war paranoia is the likeliest reason.