The S&P 500 broke the 2,000 mark for the first time in history Monday. Normally I don't get all that excited by an index eclipsing a round number, but this one was a little different.

You see, the low from the bear market in 2009 was 666.79. With the action Monday, the S&P 500 has now officially tripled since that low five years and five months ago.

Gaining 200 percent in just over five years makes this bull market one of the strongest five-year periods since the S&P 500 was launched in 1950.

Given the strong bullish trend, it isn't surprising to see the sentiment indicators skewed sharply toward the bullish side.

The AAII Sentiment Survey for last week showed a bullish percentage of 46.1 percent and a bearish percentage of 23.7 percent, putting the ratio at 1.95. This is the second highest ratio of 2014.

The 21-day moving average on the CBOE Equity Put/Call ratio fell to 0.6362, the first weekly decline in the moving average since the first week of July.

The CBOE Volatility Index (VIX) fell another 12.8 percent last week, and it has fallen more than 35 percent since it peaked at 17.57 last month.

When you have as strong a bull market as we have seen in the last five years, it is normal to see bullish sentiment. What you have to be concerned about is when investors get too optimistic.