Hi Erica,
I believe the private replies were only to keep the information in the actual signature more private.
While I tried the suggestions including doing it from a Mac, nothing worked. However, after many tries and a whole lot of copy/paste what did end up working in the end was writing my preferred signature in Word making sure to take off all formatting and
special characters you may have added to the signature, pasting it into the "personal signature" field, highlighting it all and selecting "plain text" on the drop down menu on the right in the formatting bar of the screen.
It allowed me to save it finally! Then I went back and added back the formatting I wanted (my name in bold and a couple of hyphens) one by one and it saved that as well.
Hope this helps! Maybe after you try it you could write your results for others who may be experiencing the same issue. I am not actually sure whether it was what I did or a fluke that allowed me to save it after many tries, but I suspect it was an automatic
change between rich and plain text between my first signature and my edit that blocked the system... who knows! Hopefully they'll clear all this up.
Good luck!