On “cross yourself in Alma 39:9, we have the following helpful note from the Book of Mormon Critical Text:
(cf OED C, 1194-5, mns 3, 4, & 14, vow, cancel, oppose); cf 3:15-17,
II Ne 9:18, Jacob 1:8, Ex 12:22-23 (lintel and two side posts “mark a mark”—not
in 1828 Phinney or 1979 LDS KJ [literally “X an X” on forehead]), 5, Job 31:35
(Heb taw “X” = KJ “desire” = RSV “signature”); see also protective and condemnatory
markings in Gen 4:15 (Heb ‘ot “mark, sign, token”), Rev 7;2-3, 9:4,
1316-17, 14:1, 9, 11, 15:2, 16:2, 19:20, 20:4, III Macc 2:29 (Greek xaragma
[II Macc 6:7] Sumero-Akkadian has the same X-logogram and forehead marking, Chicago
Assyrian Dictionary, VII:254; . . . ) (Book
of Mormon Critical Text: A Tool for Scholarly Reference, 3 vols. [Provo, Utah:
Foundation for Ancient Research and Mormon Studies, 1987], 3: 763 n. 964)
With respect to the Chicago Assyrian Dictionary, here is the entry from 7:254, referenced above: