New Pornographers - Sat night

Based on my experience, it's the band's tour manager, soundperson, etc and not the club which are in control of the house lights and sound when the band is on stage. So in the case of the NPs it was their soundguy who brought up Xanadu as the outro music which indicates the band is done for the evening. Unless it's planned very few bands do second encores, and the Sleater-Kinney second encore was the exception to the rule. If fans want second encores they need to demand them, but it will more than likely fall on deaf ears.
Originally posted by Darth Ed:

There's only been one occasion that I can recall of a 9:30 Club audience not giving up once the house lights came on and that was Sleater-Kinney's final show at the 9:30 Club. The house lights came up, but the audience just wouldn't have any of it and "forced" the band to come back on stage. So it is possible, just rare.
This just happened at the Spoon show. Clearly the band had only planned one encore, and the lights on the sides of the stage came on (those really bright flourescent ones), but the band came out for a second encore. At least half of the crowd had left, so it was super cool.
Originally posted by MyraEllen:
Letter to an Occupant was on their set list as the last song of the encore, and it was requested by an audience member and Carl said they'd play it later and they never did :(
The songs on the setlist for the encore were marked as "possibilities," or something like that. But Carl's earlier comment about "bad politics" made me think they'd play it, too. Oh well.