First way to do that is to look at the breadth of the market.
MEGA B: Some things to take notice of the up-volume and advancers has been declining since the big push up. The volume and advancers show that there was a large push up but has fizzled since the intial push up. Almost as if they were a stock it would have been a gap up and chopped around.

$NYAD- We had an up-day but yet the NYAD ticked down. Confirms what the MEGA B shows about advancers slowing down

$NYUD-This confirms with MEGA B that the advancing volume isn't as powerful during the first part of the rally.

TICK- Notice how the tick has been above 1000 for a while but it's highs have been getting lower. This confirms with MEGA B that the powerful move up has been fizzling.

MEGA-
$SPXA50- Still at a very high level.
$SPX200- This is still very bullish and has had its highest gain on Friday. This could indicate that a lot of stocks when they get to their 200 are breaking either buy buying or short cover. I would go with short-covering.
VIX - at such low levels. Is fear completely out of the market. Doesn't it seem like a few months ago Cramer was going to sacrifice his first born for the market to go up. Is the economy really fixed in a couple of days?
$NYMO-Its make or break, if we have an up day would should move into the overbought. Depending on the move down $NYMO could just chop around. The market would need a big down day to make some new lows on the $NYMO
Overall, the rally still looks like it is slowing down. I am short right now, I expect some more upside acutally but my out is 885. It is also possible that the market could be consolidating before another move up. SPX has tested resistance levels and blasted through them during this rally but has yet to test support levels. The SPX needs to at least test some of these support levels to see if the rally has legs.
ST=DA BEARS
IT=DA BULLS(if support levels can hold)
LT=DA BEARS