This is a recent development and I'm not sure what's going on. It seems to happen when I use my MBP and it syncs the mail prefs to MobileMe including signatures. Then my iMac loses the signature. In the mail prefs signature pane, the left column where the accounts are shown, the accounts show the assigned signatures. The problem is in the Choose Signature dropdown menu, where it loses the chosen signature and defaults to none. Any thoughts? Thanks in advance.