"What are you thinking of?" "What are you aiming for?" Are these wrong?

Not as far as I and most others who speak and write English are concerned, but starting with Dryden, there has been a vocal minority who assert without evidence that those sentences are solecisms. (NB, I am not collecting these wrongheaded rulelets for some prescriptivist nosegay, I just want to catalog the ones still extant.)

Ceci n'est pas un seing.