You may remember that classic line from the series Hill Street Blues. Each morning, as he concluded his morning briefing, Sargeant Phil Esterhaus reminded his officers of the importance of staying alert and being careful.This may be very timely advice for investors as well. I got to thinking about this as the market closed today. Why? Because, as of today's close my personal portfolio is at an all-time high. That in and of itself is not unusual. U.S. market averages are also at all-time highs. In fact, the Dow just posted its 9th straight record close. What is a little unusual is that I have now achieved new all-time highs for 10 straight days. And what THAT means is that there is an unusually low amount of volatility in the market. Think about it for a minute. Would you agree that there is currently what can only be described as a higher-than-normal level of volatility in the world? Might you even go so far to describe it as fear and uncertainty? Normally, markets hate uncertainty. What might that mean for you, and your portfolio? I could offer my thoughts. Instead, take a look at these recent comments from Art Cashin and Goldman Sachs. Let's be careful out there