Recently, a small program called DSD+ released a free version of the software allowing following of digital trunked radio systems with only one sdr dongle. Previous versions of this program required two dongles in order to effectively follow the trunk transmission and voice transmissions simultaneously. I've been playing with it at home, monitoring the ski resort, power company, and most interesting to me, the public safety radio network.
Alaska Land Mobile Radio (ALMR) is a P25 Phase II/TDMA VHF radio network covering most of Southcentral Alaska, up to Fairbanks, and down the panhandle to Juneau. The municipality of Anchorage has a complimentary system, referred to as Anchorage Wide Area Radio Network (AWARN) on 700MHz covering the Anchorage borough and networked with ALMR to transparently pass traffic. It never fails to surprise me how much information leaks out of the system. As shown in the picture above, each site advertises who it is, who their neighbors are and what frequencies their control channels are, and shown in the picture below, the health of the network.
Even if a voice channel is encrypted, the network will still tell you what radios are in the area based on who is subscribed to that particular repeater, and who is talking to who, since by necessity each radio has a unique ID number. While I don't have a transmit capable sdr to verify this, I have read of attacks where individual radios respond to spoofed network pings without notifying the user. Such an attack would make DFing of a targeted radio trivial with a transmitter and a Kraken, although the attacker would have to have done their homework beforehand and be transmitting themselves, opening them up to potential counter-attack.
Another potential attack vector would be what amounts to a wifi deauth attack, where a jamming station monitors a site or multiple sites for subscription requests and immediately sends a corresponding unsubscribe request, effectively conducting targeted jamming of a repeater at a lower power level than dumb blanket jamming.
All of this would constitute comparatively sophisticated attack vectors. To date, I am unaware of any such attacks occurring in the wild.
