You get $15 per signature on the west coast!!!  We only get $5 here in VA.  Up from the $2 it used to be in the 1990s when my mom worked in the records department at the PD.

I have no authority other than Section 1402(c)(1):

https://www.law.cornell.edu/uscode/text/26/1402#c_1

Trade or business
The term “trade or business”, when used with reference to self-employment income or net earnings from self-employment, shall have the same meaning as when used in section 162 (relating to trade or business expenses), except that such term shall not include—the performance of the functions of a public office, other than the functions of a public office of a State or a political subdivision thereof with respect to fees received in any period in which the functions are performed in a position compensated solely on a fee basis and in which such functions are not covered under an agreement entered into by such State and the Commissioner of Social Security pursuant to section 218 of the Social Security Act"

I would guess that, as long as the notary can properly account for the income (and they're probably required to keep log books), it should be exempt from SE tax, regardless of the attorney "day job".