If users were counting words/characters using this thing to fill their sig quote that would mean they would stop being a natural poster. There is a possibility that they would fill that 300 characters count and stop there.
Just my two cents.

Anyway, good job mate! Keep building these tools. Wishing u good luck.
My thoughts exactly. During my 10 years here, most of time I've been part of various signature campaigns and I can't remember myself counting words or symbols in my post. Why I would need it? I never thought whether my post is long enough or not to be counted by manager. But maybe for these who are looking into signature campaigns as one form of labour, it might be useful.
So, this script isn't for me, but still I think that OP have done good job. By making such thing he is gaining more experience as developper.
I agree. Although the tool and information are generally useful, I don't feel the need for this type of resource.
Perhaps the aspect of predicting reading time is the most interesting, especially for the reader.
Either way, congratulations on the script and keep up the good work.