I generally take a dim view of old-timey technical indicators, perhaps they work for some people but I have found there are much better tool available. One exception is divergence, which in this case is when price makes a new high, but the MACD (or your favourite oscillator) does not.
There is very nice looking divergence on NDX, and it also shows up in a weaker form on SPX and INDU. I never take it as a trade signal by itself, but it does make me look a little closer. I have marked off some previous occurrences as well. It does not give any indication about when a sell off may occur, or how much of a sell off will eventuate. Pretty useful isn't it?
Another form of divergence I take note of is the marked failure of RUT to make it back to its recent highs, which differs from NDX/SPX/INDU.
You can also see in the charts above that volume has been declining, especially over the last 4-5 weeks.
I do think we are in a long run bull market which still has a few more years to go. In the event of a shorter term sell off I would generally be looking to buy dips.
A good sign of a bull market is shrugging off negative events. We've had some reasonably serious geopolitical happenings, the invasion in Ukraine, a coup in Thailand, and anti-Chinese riots in Vietnam that produced a number of fatalities.
Struggling to think what a catalyst might be, perhaps some unpleasant surprise regarding QE tapering, or unconstrained collapse in the Chinese property market, both of which I think are pretty unlikely
There's a bunch of macro data out next week, and Apple is having its WWDC. Apple used to make up a very large amount of NDX, something like 24% of the index value was determined by AAPL prices. I know they rebalanced it and am not up to date with where it currently stands.