The speaker describes themselves as something torn, tattered, and thrown aside, then walked over by someone with dirty feet. The title, "HisSiren," run together as one word, hints that the speaker belongs to "him" or was once a lure for him, though the poem never says so outright. What we do get is the damage: the speaker's blood is "unseen," so the hurt is invisible, probably emotional rather than physical, yet it still stains the other person's soles.
The ending is the most striking part. Melting snow washes the stain away, so the evidence of harm disappears and the one who caused it is left clean. The broken line breaks of "drip-/ing" and "melt-/ing" slow the poem down, as if the speaker is watching the traces fade drop by drop. The mood is quiet, bruised, and resigned. There is hurt here, and a sense of being forgotten, but little shouting, only a cold, lonely stillness.