Thumbprints are a state rule, not a federal one
Thumbprint rules are set by each state. Many states do not require one, so check your handbook first. See what goes in a journal.
California: real-property deeds and powers of attorney
California requires the signer's right thumbprint for deeds affecting real property and for powers of attorney. Exceptions are trustee's deeds on foreclosure and deeds of reconveyance (Gov Code 8206(a)(2)(G)). Source: California Notary Public Handbook. A civil penalty of up to 2,500 dollars is mentioned for failure to obtain it . See California.
Arizona: a limited requirement
Arizona has enacted a limited thumbprint requirement, per a trade-press title, so verify the details in A.R.S. 41-319 . See Arizona.
Inkless pads and phone capture
Whether an inkless or phone-captured print is accepted depends on your state, and we have no cited rule . Notary Journal has a thumbprint entry feature, so ask your commissioning office first.
If the signer cannot give a thumbprint
Your state may give a procedure for this. We have not verified one, so check your handbook .
Ready to keep your entries in one place? Get the iOS app for Notary Journal, a notary journal and fee and mileage log for iPhone.
Not legal advice. Check your state's notary handbook or commissioning office before you rely on any summary here.