Lyric discussion by luv_burns_me 

the line 'i'll wear a shield' is referring to the k records logo which he (kurt cobain) has tatooed on his arm.

Might also be a police badge ("arrest myself"), which are usually shield-shaped

@luv_burns_me No it's obviously about him telling his first girlfriend, not the girl in Bikini Kill, his true first girlfriend, that even though he's slept with other girls he wore a condom. The whole song explains to her how he cannot be the only for her. Same as he does in About a Girl.

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