The most instantly recognisable shape for a pepper mill is the classic "chess piece" shape which in the influence map above is the light brown one in the bottom right hand corner.
The pepper grinder, which is the small silver one at the top with the glass bottom, has a squeezable trigger on it instead of a turning head which would allow for use as a limb for more of an expressive character but I'm not sure if it satisfies the criteria of pepper "mill".
The large squat looking one in the middle is a turkish pepper mill. It's turnable handle is it's main distinguishing feature and I think it could work rather well to express character as maybe a head or a limb or even a decorative accessory such as a hat or a cigar. Also being the least Penis-like shape of all the mills I've seen I think this one might be the right choice.