Its definetely an effect of sorts, it appears in the group of effects NPCs in the Debug room (I'll get round to writing that eventually), but it that effect adder/remover is just the one for the drum effect, and its part of the same sprite sheet as the drum can in ,as you know(710_charset_doramukan)
Considering the some Effect NPCs (or the ones that are versions of Urotsuki anyway) play the animation for using the effect I would say its reasonable to assume that the sprites in question are just the unimplemented result of using the drum effect.
I did think the thing the sprites are holding seemed like a shamisen at first, but you're probably right, so much room for subtle music puns (drum and bass, Rock and roll, ill stop now)
On one final note of interest, there are 3 WIP constuction signs next to the effect NPCs, one which gives (japanese i cant copy over 34), another which gives the same as the first but 35 instead of 34, and one which gives a useable wolf+bike combo, so i guess that might mean 2 new effects headed our way in future versions?