Curious - how is it barely trending? Using which method and what timeframe/lookback period?
Just a quick visual on the daily/weekly chart shows that the S&P have been trending higher most of the time since 2009, yes?
How to define a trend is an interesting question though. i would not want to use a trend line, but a mathematical definition.
One way could be to compare the # of days net positive/negative and compare the averages. If I randomly select the last 100 trading days on ES (small sample size, I know, but just for a fast illustration):
61/100 days = positive net change
Average change = 0,12 %
Average positive net change = 0,50 %
Average negative net change = -0,48 %
An even simpler way may simply be to measure the price difference close to close. That would be 382,25 or 13,18 %.
Another way may be a simple MA. For the last 100 days - the ES closed above the 20-Day SMA 81/100 days.