Two years ago I became a Notary Public in the District of Columbia. While my husband chided that becoming a notary is "what nerds do when they grow up," I contended that this was a natural extension of my role as a steward of authenticated information.
As the District's Notary handbook attests, the role has evolved from that of designated notetaker to one "certifying the truth" by witnessing signatures on important documents. I knew that my organization often had a need for this service, and I correctly predicted that becoming qualified to fulfill this role would help me get to know my coworkers. It's a public service you can provide that fits well with other solo/embedded duties as part of working in the 'white spaces of the organizational chart.'
You may find that a member of your finance staff is already a Notary Public, but often the documents that need to be notarized are financial in nature and so a third, disinterested party is necessary to witness signatures. I've also been pleasantly surprised by all the non-work/personal business I have received in my office, now that people know I am a Notary Public. I have probably notarized documents for half our staff and only half of those were work documents. It's been a great way to get to know people, and for them to get to know me. (I have the "Notary Public" nameplate on my desk so people know when they walk by that I can provide this service.)
Requirements vary state to state, but you will likely have to go through some level of training, provide references, get bonded, and buy your stamp(s) before you register with your state and take your oath. And, yes, you will be offered many additional customized products when you buy your stamp. But, yes, you can write off your set-up expenses on your taxes, as well as any income you make as a Notary Public (in fact, you have to declare that). While this is not a huge money-making enterprise, it's a nice complement to other skills, talents and certifications that librarians naturally have, and it's a great way to enhance your visibility in the workplace. It could be the starting point for long-term work relationships, and when people see you as a competent and trustworthy agent of the state, they tend to think of you as a resource for other matters. It's also a great way to learn about local and state laws, legal documents, and other procedures handled by state government.
Although I moved to Maryland after starting my commission as a DC notary, my employer wrote a letter on my behalf to the Office of Notary Commissions and Authentications so I could continue notarizing in DC until my commission expires in 2013, noting that this was a valued service I provide to the organization.