The yield on three-month Treasury bills notched up on Monday, a signal that interest rates will likely continue to rise on various forms of short-term savings. The three-month T-bill was up 0.06 percentage points to 4.82% at the weekly auction, the six-month bills rose to 5.49%; and one-year bills reached an even 6%. The higher yields will help boost the return on money market funds that invest in government securities. And if you have enough money to invest, you can also buy Treasury bills directly. For information, write the Bureau of Public Debt, Treasury Department, Washington, D.C. 20239 or call 202-452-3946. The minimum investment is a hefty $10,000. But interest on the bills is exempt from state and local income taxes, which boosts their after-tax return for many buyers.