There is description of a check that somebody gave Clark as a gift. But it was uncashable because of the sign. Therefore the cheque was of no use. Here question may arise why the writer has given the description of a cheque which is uncashable? I think the writer has tried to show by this uncshable cheque that though there are some things which can be enjoyed and used but because of some hindrances human being can not utilize them, cannot enjoy them although they have strong desire to do so. Here the sign is the hindrance for getting money.