I encountered this phrase in Wikipedia http://en.wikipedia.org/wiki/Esben_and_the_witch
His brothers did not stand to attention for Sir Red...
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Stand at attention or stand to attention both mean "assume a military posture of motionless alertness". You may also see come to attention (but never *come at attention). In the context you provide it means the brothers did not show militaristic respect for Sir Red.
At attention (rather than to attention) is a military posture, and is in effect a form of salute.
As such it is a conventional way of showing respect, often used when somebody senior enters the room.