Watch Art Cashin: Nobody rings a bell at the top

Art Cashin says investors needs to be a "little cautious" about stocks even as the rally continues.

Cashin, UBS' director of floor operations at the NYSE, told CNBC's Bob Pisani around midday that "nobody rings an audible bell at the top" of the market.

He continues to be concerned about "divergences," including the fact that the leadership is narrowing with fewer stocks advancing.

Cashin suggests viewers watch 1755 on the S&P as a possible trigger for bigger losses and says the index needs to rise to 1777 for a break-out higher.

Cashin also noted the Twitter IPO has generated big trading volume in its first day.