Subpart C of Regulation H applies to member banks who act "as transfer agents, registered clearing agencies, or sellers of securities under the Securities Exchange Act of 1934." Section 208.34 of this Regulation outlines the recordkeeping requirements for certain securities transactions effected by State member banks.
Link to the regulation: https://www.ecfr.gov/cgi-bin/text-idx?SID=2240159c84d2d3b48422a5185ff69dea&mc=true&node=pt12.2.208&rgn=div5#se12.2.208_134