I don’t read every post of every thread I participate in. Sometimes I start with the last post and work backwards. There are probably many others who do the same thing. People who read threads backwards or skip around might possibly be deprived of seeing our sigs on threads if we didn’t include it.
Now, I’m sure my sig is exactly the kind of rubbish that annoys you. Although I rarely have more than one post an a single page of a thread, when I do it takes up multiple lines.
You’ve got to understand, sigs are a form of intellectual vanity. We want someone to take notice of how clever, or knowingly moronic (reverse-clever), our signatures are. Ideally, an entire thread will be started to discuss what we’ve written, parodied, or quoted. At the least we hope someone, sometime will gratify our vanity with a side comment.
But in my case, the main reason for having my sig in every post is not intellectual vanity. That’s just why I wrote my sig, not why I repeat it. The reason I repeat it is mental laziness. I don’t want to have to think about whether I should opt to not include my sig or not. And what if I post two posts close together, but then it turns out my new post is actually the first post of a new page and I had not included my sig? Then my vanity would require me to go and edit my post, which would be far too much effort.
So, for the sake of my vanity and laziness, I post my sig in every post I make rather than judiciously.