At the end of the day attendance is for your own good. More often that not, lecturers and hence the university dont actually care if you don't attend. However, in many modules if you fail, they may only allow you one resit if they believe your attendance was not satisfactory and you havent made a serious attempt.
I sleep in quite a bit and no one has ever said anything to me.
However, there's little point just getting people to sign you in if you aren't going to make an effort to pass. Also it is annoying for other students who have to sit there watching while people go through pages of the register looking for people's names!
And I doubt that they actually would check your signature - we're not children who need to be forced to go to a lecture and get 'told off' for not going.