It means nothing. If you look at past price and volume action it's all over the place. Prices and rise, fall, or flat line with falling volume.
To me, it indicates that this up movement is NON-Dominant and we are awaiting the return to Dominance (Down) where we will see Volume Increasing.
It means there has been diminishing futures BUY side participation as the market has traded higher.....why BUY at high retail pricing levels when there was ample support levels (865's to 868's and 975's to 978's) on the way up these past months to catch this rally.
It's being accumulated ahead of news... Are there unusual volumes in the options? Usually insiders play the options, the gains are way more...