Genesis 38:18

And he said, What pledge shall I give thee? And she answered, Thy seal, and thy mantle, and thy staff which is in thy hand. And he gave (them) to her, and went in with her; and she conceived by him.

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, 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), 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), concerning which he says, “And they shall spread the shashifa,” because this is the sudar referred to in the Talmud.” See also Ramban to Deuteronomy 22:17. through which virginity is established. So did Jonathan ben Uziel translate hama’ataphoth (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, and it is further written, The sceptre shall not depart from Judah. It was these that he gave into Tamar’s hand.

חותמך, your ring.

פתילך, your outer garment,

ומטך, and your staff. She asked for three items none of which were necessary as garments for Yehudah, but were merely decorative, lending Yehudah a better image among his peers.

ופתילך, your closely fitting sash. The items Tamar chose as pledge were all things which testified to the superior standing of its owner in society. We know from Job 38,3 that a sash is evidence of someone’s manhood, i.e. someone’s superior status. She wanted to own such trinkets reminding her constantly of Yehudah’s status so that her child would be influenced by the thoughts she entertained during her pregnancy and would grow up to be like its father.

חותמך, as per Onkelos, the signet ring.

ופתילך, your outer garment, cloak, as per Onkelos, שושיפך. Or, what is meant is the turban, i.e. a status symbol. In Numbers 19,15 the expression צמיד פתיל, “a tightly fitting lid,” describes a vessel of contours similar to a turban. The expression also occurs in the Mishnah Shabbat 28, as well as in verse 25 in our chapter [because of the plural mode, Ed.] it appears to describe attire each composed of two different cloths and colour.