You can think of one small sheet of paper put into your hand, and it settles something. It once came printed in pink, and the colour ended up in the name. What the paper decides depends on who hands it over: the office that ends your job, or the office that says this car is yours.
pink slip 可以想成「別人遞到你手上的一小張紙」。pink 是粉紅，slip 是小張紙條，早年有些單位真的用粉紅色的紙印，後來顏色不一定了，名字卻留了下來。這張紙上寫什麼，要看是哪個單位發的：可能是公司說你的工作到此為止，也可能是監理單位說這台車是你的。
From the word’s history
Wiktionary traces the name to the colour of the paper, a practice of the past that is not necessarily kept today; it notes the car-title sense most likely comes from California, where the title was printed on a small pink card.
Wiktionary 說這個名字來自紙張的顏色，那是過去的做法，現在不一定還是粉紅色。車籍那個意思很可能來自加州：當地把所有權狀印在像索引卡大小的粉紅色紙上，其他州多半用藍綠色的整張紙。
Wiktionary, "pink slip"
登入就可以看每一支怎麼連回核心畫面。