The rules are there. When you signed up, you agreed to abide by them.
When people see a sig that is too big, they usually will make a remark about it. But there are no rules stating that warnings will be given.
Warnings used to be given for this, but some people decided to be anally-cranially inverted. Thus, the practice was dropped.
Besides, once someone has lost the priveledge and then got it back, they usually don't violate it a second time.