"You'll know it's the 'big top' when millennials start buying," Bank of America (BAC - Get Report)  analyst Michael Hartnett said in a note Friday.

Millennial investment is the classic late-cycle signal. Millennials have only 30% of their assets allocated to equities, whereas older age groups have 46%. Once the catch-up begins, the market could be nearing a peak before a downturn, according to Business Insider.

The uptick in mobile trading platforms might stir more millennials to invest in equities since they already spend a great deal of time on mobile devices. Most millennial trades skew toward futures and derivatives, TD Ameritrade (AMTD - Get Report) Director of Trading Victor Jones said.

Hartnett said the end of this bull market won't all be on millennials, though. He cited one of Berkshire Hathaway (BRK.A - Get Report) (BRK.B - Get Report) Chairman Warren Buffett's favorite indicators - U.S. stock market cap as a percentage of nominal GDP - as another key signpost before a downturn. That figure is currently on pace to hit an all-time high.

What's Hot On TheStreet:

Well OK then, Jeff Immelt: General Electric's (GE - Get Report) outgoing CEO Jeff Immelt had some choice things to say at an event in NYC on Thursday night, TheStreet's Kinsey Grant reports. First, Immelt revealed a possibly fatal management mistake Kroger's (KR - Get Report) CEO might have made about Amazon (AMZN - Get Report) who as we all know, just inked a $13.7 billion deal for organic grocer Whole Foods (WFM) . Immelt then took a jab at Hillary Clinton and Barack Obama for not visiting factories in their push to lift manufacturing wages. Talk about a well-paid boss going down swinging.

Why Sears Canada is dying: Sears Canada (SRSC) has one foot in the grave just like its ailing U.S. friend Sears Holdings Corp. (SHLD) . Unfortunately for Sears Canada, it's that friend across the boarder that has played a large role in its demise, TheStreet's Michelle Lodge reports. Sears has sucked badly needed cash away from Sears Canada through the years, leaving it unable to upgrade stores and do other things to compete effectively in the always challenging Canadian retail market.

General Electric is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells GE? Learn more now.

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Editors' pick: Originally published June 23.