Concept Album: Possibly Shouso Strip, despite the fact that it features three A-sides. Its first six tracks deal with some sort of crime, and the last six deal with some form of punishment. The middle track is titled "Tsumi to Batsu" ("Crime and Punishment").
Creator Thumbprint: Symmetry. Just look at the track listings for most of her albums to see an example.
It's worth pointing out that not only are the number of characters in each song symmetrical, but frequently the scripts used are symmetrical as well. For example, the first and eleventh tracks on Kalk Samen Kuri no Hana have two Kanji characters in their titles, while the second and tenth have eight katakana characters, and so on. Even when the characters themselves aren't symmetrical, she'll sometimes make the track listings symmetrical in other ways; for example, the even-numbered track titles on each disc of Utaite Myōri ~Sono Ichi~ are written in English, while the odd-numbered ones are in Japanese (which does not always match with the language(s) sung in the songs).
A Date with Rosie Palms: The PV for "Tadanaranu Kankei" certainly has... suggestive imagery. Nothing explicit, but considering the large amount of wasted tissues and Ringo's penchant for Double Entendre...
Fake-Out Fade-Out: Inverted by "Izonshou," the last track on Shouso Strip. The song ends with a three-minute instrumental section, which begins to fade out over the last minute—and then the music is cut immediately, when the album reaches the 55:55 mark.
Iconic Item: Her mole. It was still part of her character long after she got one of them removed.
Live Album: The first CD of Zeccho Shuu, Tokyo Collection, and Mitsugetsu Shou.
Loudness War: Except Muzai Moratorium, practically every album she's made (solo or with Tokyo Jihen) is brickwalled in some way or the other, with Shouso Strip being the worst offender. Considering the amount of control she has over her music and her eccentric personality, it can be argued that she does it on purpose.
Lyrical Dissonance: Considering the broad variety of her songs, this was bound to pop up. "Aisaika no Choushoku", "Zettai Zetsumai" and the album version of "Yattsuke Shigoto" are particularly egregious offenders.
Market-Based Title: Tokyo Jihen's album titles and the band's name is translated as Tokyo Incident's on their album covers.
Medium Blending: As noted above, the PV for "Tsugou no ii Karada" is part animated and part live-action.
Scatting: Shiina did this often in her earlier solo career.
Sideboob: Her outfit without the jacket in "Tsumi to Batsu" shows some.
Something Completely Different: In the middle of their "Bon Voyage" concert, the other band members take the stage in singing "Ice Cream no Uta". Right after that, they play the bonus stage music from Ice Climber.