Commentaire sur La Genèse 38:18

חתמך ופתילך THY SIGNET AND THY STRING — The Targum renders it by “Thy signet and thy cloak” — the ring which you use as a seal and the cloak with which you cover yourself

THY SIGNET ‘UP’THILECHA.’ Onkelos renders it as “thy signet and thy cloak,” meaning “the ring which you use as a seal, and the cloak with which you cover yourself.” This is Rashi’s language.
But it is not correct to say that he would give his cloak, and go away from her unclothed. And how is it that a cloak is called p’thil in the Hebrew language? And how can it be referred to later on as p’thilim,¹⁷⁸Verse 25 here. in the plural? Now should you say that on account of its fringed strings (p’thilim), the garment was called p’thil, far be it that Judah should fulfill the Commandment of Tzitzith (Fringes),¹⁷⁹See Numbers 15:38. yet treat it so lightly as to give it away in unchastity! Perhaps, he had with him a small scarf which he occasionally wound around part of the head, and which was called p’thil because it was short as a p’thil (fringe), and it is this which the Targum [Onkelos] rendered as shashifa, [which Rashi incorrectly took to mean “a cloak”]. Now you will not find that Onkelos will translate simlah (a garment) as shashifa wherever it is found in the Torah. Instead, he translates it throughout by a term denoting “cover” or “garment,” excepting the verse, And they shall spread the ‘simlah’ (garment),¹⁸⁰Deuteronomy 22:17. concerning which he says, “And they shall spread the shashifa,” because this is the sudar referred to in the Talmud¹⁸¹Kethuboth 10 a: “Bring me the sudar.” See also Ramban to Deuteronomy 22:17. through which virginity is established. So did Jonathan ben Uziel translate hama’ataphoth¹⁸²Isaiah 3:22. (the mantlets) as shashifa, these being small scarfs which they wound around the head, and distinguished persons spread them over their bonnets and headbands. This custom still prevails in eastern countries.
It is further possible that Judah possessed a seal impressed with the form of a lion or some other known figure, as rulers do, and he also had fringes in his hand, woven in the same design, with which to stroll about, as well as a rod in his hand, as becomes a ruler or lord, even as it is written, A strong rod, to be a sceptre to rule,¹⁸³Ezekiel 19:14. and it is further written, The sceptre shall not depart from Judah.¹⁸⁴Further, 49:10. It was these that he gave into Tamar’s hand.

חותמך, your ring.