396. 'Jehovah put a sign on Cain, lest anyone should strike him' means that the Lord distinguished faith in a special way to ensure its preservation. This is clear from the meaning of 'a sign' and of 'putting a sign' on somebody, which is a way of distinguishing him, as in Ezekiel,
Jehovah said, Go through the middle of the city, through the middle of Jerusalem, and make a sign on (or designate) the foreheads of the men (vir) who groan and sigh over all the abominations. Ezek 9:4.
Here 'designating foreheads' does not mean putting a sign or stroke on their foreheads but a way of distinguishing from others. Something similar is said in John about men who did not have God's sign on their foreheads being subject to condemnation, Rev 9:4. Here again 'having a sign' stands for a way of distinguishing.
[2] In the same book this sign is also called 'a mark', where reference is made to placing a mark on the hand and on the forehead, Rev 14:9. That which was meant by signs and marks the Jewish Church represented by binding the first and great commandment on to the hand and on to the forehead, a practice mentioned in Moses,
Hear, O Israel, Jehovah our God is one Jehovah; you shall love Jehovah your God, with all your heart, and with all your soul, and with all your might. And you shall bind them as a sign on to your hand; and let them be as frontlets between your eyes. Deut 6:4, 5, 8; 11:13, 18.
This represented the requirement to distinguish the commandment concerning love above all other commandments. This shows what making a sign on the hand and on the forehead means.
In Isaiah,
One is coming to gather all nations and tongues, and they will come and see My glory, and I will set a sign among them. Isa 66:18, 19.
And in David,
Look to me and have compassion on me; give Your strength to Your servant, and save the son of Your handmaid. Make a sign in me for what is good, and let those who hate me see and be put to shame. Ps 86:16, 17.
From all these quotations it is now clear what 'a sign' means. Let nobody suppose therefore that some sign was put on a man called Cain, for the internal sense of the Word embodies matters altogether different from those of the sense of the letter.