Definition of "speaking of"

“Speaking of by the way: nice car. I mean that.”

2006, Mark Winegardner, The Godfather’s Revenge, G.P. Putnam’s Sons, page 76

“No more songs. This is a restaurant, for Christ’s sake, and speaking of, can somebody tell me where the hell is that veal?”

2009, Wells Tower, “Executors of Important Energies” (short story), in Everything Ravaged, Everything Burned, Macmillan, page 83

— […] Speaking of by the way we should go shopping on Saturday or Sunday because Penney’s is having a sale at Fair Oaks.

2009, James Boice, NoVA, Simon and Schuster, page 47

“ […] And speaking of, can you please cover up that hideous shirt?”

2010, Julia DeVillers, Jennifer Roy, Take Two, Simon and Schuster, page 8