Some notaries have a paypal account and can get paid for jobs by credit card. Other notaries have their own credit card account and can accept credit cards. If you work for signing companies, they pay by check, but individual clients might like the option to pay by credit card. The more payment options you have, the more business you can get.
Paypal is very easy to use and many people already have accounts with them. Paypal will keep a few percent commission for themselves, but its worth it for the convenience. Paypal will track all of your transactions, so you will have queriable records for any job that was paid via their system.