Kathryn/FlickrHappy birthday, bull market!

Stocks are rallying at the start of the week after tanking on Friday.

Just a little before noon in the NYC, the Dow was up about 107 points, the S&P 500 up around 6 points and the Nasdaq up about 2 points.

It’s the bull market’s birthday today, six years since the bottom during the financial crisis.

And as stocks have rallied, they’ve become more expensive.

“The typical stock in the S&P 500 trades at 18.1x forward earnings, ranking at the 99th percentile of historical valuation since 1976,” Goldman’s David Kostin wrote in a note Friday.

In this expensive market, Kostin has three trading recommendations, including buying stocks that offer cash returns through buybacks and dividends.

There’s no major US economic data release on Monday’s calendar.

Earlier, the European Central Bank started its bond-buying program, or quantitative easing. The bank reportedly bought government bonds from several countries in the Euro area on Monday, according to Bloomberg. Bond yields are lower across the region.

Apple’s 1:00 p.m. ET event will be closely watched, as the world’s most valuable company unveils details of its smartwatch in San Francisco. Its shares are up nearly 1%. The company will replace AT&T on the Dow Jones Industrial Average later this month.

Shares of General Motors are up by nearly 3% after news that the company will announce plans to buyback shares. This follows calls from a group of hedge funds to return investors more cash.