Sentiment

Sentiment is starting to look like it frequently does at other highs.

Sum
Put-call daily extreme & weekly low value, ISEE higher value but not extreme yet, NAAIM extreme, AAII recently some extreme depending on timeframe. All this is enough to limit upside and increase risk of shakeouts. 

Put-call (CBOE standard put-call ratio with 10MA)
Daily view - only a handful of days lower in last 2 years. 

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Weekly view
Not as extreme but still on the low side in terms of number of weeks from 2011 below last week's value. 

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ISEE
MAs still subdued but 12/8 reading highest since 10/10 and among higher values of 2016.

NAAIM
2nd highest reading of all data going back to 2006 2H.
Other top ten, along with rough weekly results on SPX

1/30/2013, 104 - 4 week stall in otherwise QE fueled melt up
11/27/2013, 101 - 2 weeks sideways then down
7/27/2016, 101 - price level near key high, upside limited
12/11/2013, 100 - middle of pullback low, 2 weeks up then another drop
3/1/2007, 100 - actually quite correct, big buying after first drop in 9 months
1/3/2007, 100 - no damage, market continued moderately higher
2/25/2015, 99 - price level near major highs, not significantly higher over several months
12/26/2013, 98 - next move down
8/17/2016, 87 - near level that was high for about 3 months

12/8 - 101 ? 

AAII
Reached more toppy levels 3 weeks ago, which has been quite correct. Still, as of then, 

Data from 2005: 14% percentile (meaning only 14% were higher than this one)
Data from 2010: 12% percentile
Data from 2012: 10% percentile
Data from 2014: 7% percentile
Data from 2015: 3% percentile
Data from 2016: highest value