irb> Iconv.conv('shift_jis', 'utf-8', "\302\273")
Iconv::IllegalSequence: "\302\273"
irb> Iconv.conv('cp932', 'utf-8', "\302\273")
Iconv::IllegalSequence: "\302\273"

» (» 、RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK (U+00BB)、終わりギュメ)
を含むUTF-8文字列をIconvでShift_JISっぽい文字列にしたいんですが…