EW (?) operation against train system in Poland. Hijacked frequencies cause disruption (emergency RADIO-STOP signal emitted), and... Russian national anthem, and Putin's speech. Developing. Weird things start to happen. Requires physical proximity. https://twitter.com/PKP_PLK_SA/status/1695244539819090343
There was a case 10~20 years ago of a teenager who started triggering emergency stop for fun using self-modified radio equipment. I was actually surprised that no vandalism-leaning person did something similar in a massively disruptive way (by hiding multiple transmitters and doing so in a well-chosen location), so I wouldn't exclude the vandalism hypothesis yet.
BTW. The physical proximity requirement is not that strong: the range is limited by terrain and R^2, and fixed transmitters of rail dispatchers have a range of iirc small tens of km. I would wager that using a transmitter with ERP of 100W or so from a good vantage point would give you at least as much.
