I'll be negative whenever I want. In fact, I'm not being negative. I'm just answering the question.
Sure, there's no rule keeping someone from putting spaces in their siggy to make it bigger. What there is is COMMON SENSE. I accidentally made my sig too big one time on here without even having a picture at all. The mods jumped all over it--I got like four PMs in a matter of two hours.
Maybe there's not a "written" law about texts in your sig, but if it gets too long for any reason the mods will use their common sense and tell you to fix it.
The pictures in the signatures are big enough.