The Coinbase Bitcoin Premium Index has turned negative again, registering at -0.0022% after five days of positive premium, according to Coinglass data on March 19. This shift follows a period in February when the index was negative for 40 consecutive days. The index measures the price difference between Bitcoin on Coinbase and the global market average, serving as a key indicator of U.S. market sentiment and capital flows. A negative premium suggests stronger selling pressure and reduced investor risk appetite in the U.S. market.