locus sigilli (loh-k<<schwa>>s si-jil-I), n.[Latin] The place of the seal. • Today this phrase is almost always abbreviated “L.S.” These are the traditional letters appearing on many notarial certificates to indicate where the notary public’s embossed seal should be placed. If a rubber-stamp seal is used, it should be placed near but not over this abbreviation. See NOTARY SEAL . [Cases: Seals  3. C.J.S. Seals § 4.]

“For some period in history seals were required to consist of wax affixed to the parchment or paper on which the terms of the instrument were written. The wax was required to have an identifiable impression made upon it. Usually this was made by a signet ring. In time when ordinary people, who did not have signet rings, learned to read and write, it was to be expected that substitutes for the traditional seal would be accepted by the law. Thus, today it would be generally accurate to say that a seal may consist of wax, a gummed wafer, an impression on the paper, the word ‘seal,’ the letters ‘L.S.’ (locus sigilli) or even a pen scratch.” John D. Calamari & Joseph M. Perillo, The Law of Contracts § 7-3, at 296 (3d ed. 1987).
[Blacks Law 8th]