When Hydra was raping/torturing Bucky, they liked adding insult to injury by carving the names they'd call him into his skin.

So maybe they'd carve "filthy whore" on his chest, or "cocksucker" on his cheek.

Maybe other stuff, too, like "insert cock here" on his lower back with an arrow pointing down. Really, the filthier the better.

The serum would make it fade, in a few days, but he'd have it on his body long enough for it to make him feel dirty, and to remind him of his rapes for days on end.

Also possible aftermath where Bucky still feels like those words are visible on his skin, even though his skin is unblemished in that way, and just can't scrub clean. He thinks everyone will be able to see he's a dirty whore by just looking at him.

Bonus if one of the guys doing that carving/raping is Rumlow.