The Batsignal is off when he does it, and it's during the day when it's cloudy and/or rainy.
I interpreted it as a PR move. Simply unplugging the signal doesn't really send a message, to Batman or to the public or whatever. Smashing the symbol to bits kiiiinda does.
Exactly. Gordon might be forced from "behind the scenes" to perform such a public display of "we don't condone vigilante justice!" and does this as some sort of PR stunt/media event, "to send a message".
His heart probably isn't in it, and I'm sure, in context, the scene will eventually make sense (maybe he calls Batman beforehand and say "hey, if you turn on channel 4 this afternoon, don't be pissed at what you see...I'm just doing it to get the mayor and the 'criminal's rights' crowd off my butt a bit; it's no reflection on how I feel about you...").
t:
Big city politics and all...
I figure by the time the events in this movie are going down, Batman and Gordon both realize they've really only got - and can trust - each other.