What does "check" mean in "check your privilege"?
Solution 1:
Here it is being discussed on The Guardian...
roughly speaking, ["check your privilege"] is a way of telling a person who is making a political point that they should remember they are speaking from a privileged position, because they are, for example, white, male, heterosexual, able-bodied or wealthy.
Of OP's suggested meanings for check, the best one is examine closely.The person being addressed is being told/reminded that he should consider carefully whether the opinions he's expressing might perhaps owe more to his privileged perspective than to objective reasoning. Obviously in practice the strong implication is that the speaker invariably thinks it does.
As @Janus comments below, it's perfectly possible to interpret the usage as a combination of OP's #1 and #3 (leave your privileged perspective outside when you enter this discussion). It should normally be obvious from context which exact sense the speaker intends (is he giving advice before you express any opinion at all, or after you said something ascribable to privileged circumstances?).
The difference in meaning between the two is relatively small, and it's quite possible that different speakers (or the same speakers at different times) may have either "nuance" in mind.
Solution 2:
I think everyone's missing the simple answer:
http://www.urbandictionary.com/define.php?term=check
- to put someone in their place
- to realize your current position in any of many situations
- paper money you write
best check yo self, before you reck yourelf
In particular, the cited example is probably the phrase that most popularized this usage of the word check:
http://www.azlyrics.com/lyrics/icecube/checkyoself.html