[dalby]

there is no "exact" answer. but here are some hints

first of all, trend days are more likely to occur after volatility has contracted. with that in mind

1) ticks almost entirely above or below zero line
2) almost all, or all sectors strong bullish or bearish
3) large gap up/down with confirmation in breadth
4) price moves in direction of trend with strong confirming volume and pulls back with lighter volume
5) no, or minimal pullbacks in price after tick extremes
6) price blows through resistance levels without even a hiccup