MAS Notice 649 pertains to the liquidity risk management framework for banks in Singapore. However, it does not specifically mandate a minimum liquid asset ratio of 18%. Instead, it outlines the requirements for banks to maintain adequate liquidity to meet their financial obligations. This includes adhering to the Liquidity Coverage Ratio (LCR) and Net Stable Funding Ratio (NSFR) standards, which are in line with the Basel III international regulatory framework. The LCR requires banks to hold a sufficient amount of high-quality liquid assets to cover net cash outflows over a 30-day stress period, while the NSFR ensures that banks maintain a stable funding profile in relation to their assets and off-balance sheet activities. For specific details on the percentages or ratios required, it is best to refer directly to the latest version of MAS Notice 649 or consult with the Monetary Authority of Singapore for the most accurate and up-to-date information.