If you can't read why are you here?

People just don't read. You can put up all the signs you want with any attention getting colors, lights, or fonts but people will not read signs. It's not just the library, plenty of other places have problems too.

Is it that they really can't see signs, can't read, or is it because they just don't care?

For example, I once counted six "no cell phones" signs between the library doors and our Internet computers, including one by the offender. Did they still let their phone ring? Did they still engage in loud, inane conversations to the irritation of those around them? Did they still resent the librarian for pointing out the signs that says NO CELL PHONES!? Sadly they do.

Contrary to popular opinion, librarians do not enjoy shushing people. We have better things to do and not much time to do it. Pointing out the obvious to people is an interruption to the work we could otherwise be doing.

I wonder if I posted signs that said $5.00 fine for each second a phone rings or a cell phone conversation continues would be more effective?

There are only about three places in the world where you can escape cell phone users. Places of worship, libraries, and a few spots in the wilderness with no coverage. And sometimes even in these places!

Even places of worship are under siege, so I guess it's not surprising people are so inconsiderate to their fellow library patrons. It gotten so bad at catholic churches in Mexico that they've purchased cell phone jamming technology from the Israelis! ("Blocking cell phone signals in the United States is illegal, but Mexico does not yet have a regulation against it..."). Mexican churches jam cell phones for quiet Mass. The priests turn it on during mass. I'm not catholic but that seems extremely irreverent to have their cell phones on during worship. One would think their next confession would get a little rough.