Your library is very likely a portal. Resistance and Enlightened team members are hacking it, deploying resonators and mods, and linking it to other portals to create fields. And they're doing it from inside or just outside of your building using an app and their GPS-enabled device.
Intrigued? The game is Ingress, an "augmented reality massively multiplayer online GPS-dependent game" from Niantic Labs, a startup within Google. Whew! That's a mouthful.
People all around the world are participating one giant game using their mobile devices. They download an app, create an account, pick a team, and join the fun. There's a back story for the game that gets quite complicated, but it all boils down to some basic tasks: capture and control portals, link them up to make fields and control territory, earn points and badges, and increase your level and score both individually and for your team. Players can also submit new portals as long as they meet the criteria. As stated in this article, Ingress "is like a combination of geocaching and capture the flag," and it's incredibly addictive.
You're probably a portal. From Wikipedia: "Portals are typically associated with buildings and landmarks of historic and/or architectural significance such as sculptures and other public art, libraries, post offices, memorials, places of worship, public transit hubs, parks and other recreational or tourist spaces."
You may see some unusual traffic. You may see cars outside your building at odd hours with the drivers' faces lit up by their cell phone screens or see people with their cellphones furiously hitting a "fire" button to blow up the other team's resonators so they can take over the library for their team. In any case, there are folks who may be non-library users who are now very aware of where the library is.
There may be some programming possibilities. I found one library that even held an Ingress-themed program for Teen Tech Week.
Personally, I've found Ingress to be a great way to easily find points of interest when I venture to a new town. Public libraries, historic landmarks, interesting public art, and sometimes even unique local businesses --- it's great to hack and explore at the same time! (and a very clever way for Google to get the low-down on all of the cultural points of interest in a city!)