Inverted commas (or speech marks, or quotes) are sometimes used by fastidious writers as a kind of linguistic rubber glove, distancing them from vulgar words or cliches they are too refined to use in the normal way. This 'N' character in Iris Murdoch's novel evidently can't bring himself to say 'keep in touch' without sealing it hygienically within inverted commas, and doubtless additionally indicating his irony with two pairs of curled fingers held up at either side of his face.