Need more than just a standard signature? I needed to add an HTML signature to Outlook messages to comply with our company policy. Simply add a blank signature. Then open it with an editor in your host OS. Mine was located in
~/.cxoffice/{CX_BOTTLE_NAME}/drive_c/windows/profiles/crossover/Application Data/Microsoft/Signatures/{SIG_NAME}.html
There are .rtf. and .txt files there as well. I edited it there, saved it, and all is set! I even have a picture in my signature using an img tag with relative directory references.
If you have your original, Windows-based signatures on file, you can put them into the signature directory detailed above (this has been known to work, at least). If the signatures are in a zip file, you can drop the zip file into the directory and unzip from there. Outlook will then be able to recognize the presence of the signatures and you can import them using Tools->Options->Mail Format->Signatures
