Okay, guys, before you get your hopes up, I'm only posting this because I need to ask a question. I'm not "officially" back yet. 
I suppose this question is directed more at John, but if anyone else can correctly answer this for me, go right ahead!
Thunderbird reads from an external file for your signature; there's no option to directly enter one. So is there a way that I can have my signature on my key and still reliably use the file? If the drive letter changes, the absolute path that Thunderbird puts in the box after selecting a file will no longer work. I realize that I could probably manually enter a relative path; however, I'm not sure what it would be relative to, if it would even work.