Are Cheques Muktzah on Shabbos? If so, what type of Muktzah?
Sh'miras Shabas K'hilchasah 20:19–20 says they are muktzim mechamas chisaron kis (muktze because of potential loss of value), which is one of the 'severe' types of muktze, so they can't be moved even if one needs them or their spot. He doesn't differentiate among blank checks, signed checks, and cleared checks. As always, for practical halacha, CYLOR.
Blank checks are Muktza machmas Issur. This type of muktza is muktza gamur and one can't move it for any reason.
Items which have no purpose on Shabbos (or no designated purpose at all, and kept that status when shabbos arrived) are categorized as muktza machamas gufo (intrinsically muktza).
(Tom wanted to call it machmas issur because it had a designated pupose, but was unusable because using a check is forbidden on shabbos. I have seen muktza machmas issur normally applied to an item which is intrinsically purposeful on Shabbos, but the is an extrinsic issur in it's usage, like the case of a garment of shaatnez).