Not a story idea, just a part of one.
A succesful author with poor penmanship – so poor that every one of his signatures seems to be a unique abstract shape* – is asked by his publisher to sign the title pages of the last remaining cartons of his latest book so the books can be sold at a premium.
He does so. But it takes a while for them all to sell. In fact the author dies of old age before they are all sold. News of his death triggers a run on the title from book lovers seeking his last signatures. Eventually it is noticed that by the last carton, the abstract shapes of his signature appeared to have taken on resemblances to common obscenities.
The “fuck you and your mother” copy sells for one million dollars on ebay.
*yes, that part may be based on life