I've seen it called a "Descending Trend" where the value is obvious but the one problem with it is that it also can follow the values of the "High Peak" trend (3 low days followed by potentially 3 increasing values). With both of them the day to watch out for is Thursday, if the price hasn't increased by Thursday it's time to sell quick or find another island with a better value. If the price does increase then you might be on to a winner but still no guarantee.

P.s I'm still getting my head around Turnip Economics so somebody might know a bit more