One of the key indicators will be the reshuffle. Oddly, I think the more fight Brown's enemies put up to keep their favoured positions, the less likely they are to act against the PM. Why? Because one of the surest ways for Brown to trigger unrest is for him put Balls as Chancellor, while moving folk like Darling and Miliband to undesirable briefs. If the plotters fight against this, or if they cut deals to sweeten the moves, it will show that they are still somehow invested in, and bound to, Brown's government. And it sends out a weak message that the PM can prey upon - after all, why go to any lengths to defend your position in a government, if you're keen to topple that government and start from scratch?
For me, the thing that marked the would-be Labour coup last summer was its cosiness. No-one wanted to get their hands bloody, and - in the end - no-one wanted to get on the wrong side of the Dear Leader. For the sake of their own party, Labour MPs can't go about things the same way this time. Screw Brown's reshuffle - it's an irrelevance; deckchairs on the Titanic, and all that. The only rehsuffle the plotters should care about is the one which sees them get a new party leader. Watch this space.