Everyone needs a notary public at some point in their lives. Notaries serve the important function of making sure people who sign documents are really who they claim to be. And it just so happens that many legal documents also need to be notarized. So you could be a one-stop shop, right?
Well, there are good and bad reasons to become a notary, so you may want to take the following thoughts into account. (Note: much of this information comes from California, but its notary laws aren't terribly different from other states'.)
Conflicts of Interest?
It's unclear whether an attorney cannot, as a rule, notarize documents in the course of representing a client. What is clear is that notaries can't notarize documents in which they're named, or documents in which they have a direct financial or beneficial interest in the transaction. They also can't notarize their own signature.
So if an attorney is representing a party, but otherwise has no interest in the transaction, can he notarize, say, the client's signature? Probably so -- but this is potentially dicey territory. (If you are fortunate enough to be able to employ a secretary, much of the problems associated with conflicts can be alleviated by having your secretary be a notary.)
In general, notaries aren't allowed to pass normative judgment on the documents they're supposed to notarize. If they see a mistake somewhere in the document that doesn't affect the validity of the document, they're not authorized to point it out -- unless they're a lawyer.
Many states caution notaries that they can't give advice on how to fill out forms, but attorneys certainly can. That's great for existing clients, but be forewarned that if a stranger comes to you to notarize something and you start offering advice on how to fill it out, you might have a new client (not that you'd ever do something like that).
Becoming a notary costs money: Notaries must take a state-approved training course, sit for an exam, purchase supplies from an approved vendor, get a fingerprint scan, and pay for a bond. The total cost for a four-year commission (which has to be renewed every four years -- yes, with all that stuff again) can be as much as $400, according to one California notary education provider. On the flipside, a notary can usually charge only $10 maximum per signature. So it's not exactly a cash cow.
Two Liabilities for the Price of One?
If you're a lawyer who is also a notary, then congratulations, you have not only the statutory duties imposed on a notary, but an additional ethical duty imposed on you as a lawyer -- even if you're just notarizing and not lawyerizing. Consequently, if you fail to properly identify someone or improperly notarize something, then you can get hauled in front of your state bar for discipline in addition to any other sanctions.
Becoming a notary may be convenient, but don't forget that every one of your lawyerly ethical obligations extends to non-lawyer work you do, as well.