I need to pay mom's bills. I'm on her account, but her checks don't have my name on them. It is a joint account. Can I legally sign her checks, and will her creditors and her bank accept them?
If it is a joint account then you would have completed a signature card for the bank, which authorizes you to use the account as if it were your own. Many times, with joint accounts, the bank will put the names of both account owners on the checks so that it is clear to anyone accepting the check that either you or your mom can write checks on the account Creditors will most likely accept checks signed by you, although they may want to contact the bank to verify them at least the first time around.
If it's the case where your mom gave you power of attorney over the account, this could be a bit more complicated, and some creditors may balk at accepting such checks, since you'd have to include some indication that you have POA when signing the checks.
If this is a joint account then I would encourage you to spend a few dollars for new checks to be printed with both your name and your mom's on them so it avoids confusion and problems using the checks. This is the easiest, simplest solution and can help you avoid headaches.