Is it a real apostrophe (') or one of those smart quotes(ʼ) or even a back tick(`)?

What's really happening here is that there is an encoding mismatch. One part is in unicode and another part isn't. Maybe you set up your sig using unicode but are posting with another encoding. Or vice versa.

I use the Signature Switch add-on to swap between signatures and never have that sort of difficulty.

Perhaps if you paste in your signature using "paste without formatting" (ctrl+shift+v) then the pasted text will be coerced into the same encoding as the message text.

I'm not sure how to answer your question. I used Notepad to type the original into, and I just used the apostrophe on the keyboard, nothing special. I know Notepad is pretty basic, but not sure whether it's unicode or not.

However, I copied the text into my word processing program, cleaned up the mess, recopied that and pasted it into Notepad in place of the prior text, and saved it. When I went to compose a new email, my signature block was fine.

I looked at the comments and the review comments indicate that it wouldn't work for me (I like my name above my signature quote), but I thank you for mentioning it as a possible solution.

Anyway, you certainly shed the proper amount of light on the topic, so I'll be cleaning up the other signature quotes I use the same way. Thanks!

I'm glad you have found a solution, though you have gone in the opposite direction to how I'd have done it.

In my experience, word processors generate mess; look at the source of an email created in Word and you'll see a whole .dot template with complex definitions for lots of formatting options that you're unlikely to ever need or use.

I don't understand what specific ordering you seem to expect Signature Switch to impose on you. It simply inserts an HTML-formatted document into the end of your message. It can also insert a plain text version of your signature where appropriate.

Another approach is an addon such as Clippings or QuickText. Both allow frequently-used text to be inserted into a message, and some users make use of this to add a signature. It seems a lot less hassle to me than finding and opening a text file, then selecting and copy-and-pasting from it into Thunderbird.

Maybe the fact that I'm a die-hard WordPerfect user explains why my word processing program didn't f*ck things up - I expect the worst from Word and am rarely disappointed!

The reviews for Signature Switch indicate that you can't put your name above the quote, which is my preferred positioning. That's why I said it wouldn't work for me. In any case, as long as the Account Settings options operate properly, I don't really need anything else.

Also, I don't open Notepad to copy and insert a signature every time I write an email. Under "Account settings," there is the option to either insert the text of a signature quote in a block provided OR to "Attach the signature from a file instead," and the latter is what I do.

Thanks again!