Hmm, basically my top four choices are the same as bulia's.
These would be my first and second choices, respectively:
30 http://www.deviantart.com/view/19683871/ ("ad")
38 http://www.deviantart.com/view/19938100/ ("blueprint")
I'm not overly concerned about the weight of the ad one, though I'll need to have a look at the original SVG. I think there would be room for invisible optimization if the artist hadn't already performed it.
I do think the Soviet one is visually powerful, but it doesn't fit the format of the dialog well. Also, IMO, Soviet imagery has been overused in Free Software circles, and besides which it has unpleasant associations for many.
33 http://www.deviantart.com/view/19706284/ ("Soviet")
The version with the brick wall works better compositionally, even if the brick wall looks a bit unfinished yet:
34 http://www.deviantart.com/deviation/19706201/ ("Soviet flypost")
I like this one too (the glass is ... wow), although that particular green and the choice of the font for the ".42" turns me off quite a bit:
-mental