Technically, a staff member would disable it, and you'd have an orange "sig disabled" box instead. If you still don't change it, that's when a warning would happen.
It still posts the sig here even if it's too big, but it adds a scroll bar to the signature, and that's how you can tell that it's over the size limit. (Though sometimes there's a scroll bar even if the sig is in the limits. Unfortunately, that isn't the case here.)
Sorry about all this. I just don't want to see you get in trouble for something so simple!