09/05/1919
https://www.presidency.ucsb.edu...
"Principal Consular Officers shall keep at their offices a Register of all American citizens residing in their several districts."
"The Secretary of State is authorized to make regulations concerning registration additional to these rules and not inconsistent with them."
"The general principles which govern applications for passports also govern applications for registration."
"Consuls may issue, upon forms prescribed by the Department, certificates of registration good for one year, for use with the authorities of the place where the persons registered are residing."