An elementary school teacher of mine had this happen to her (this was in the early '90s, so her experience I'm guessing would have been in the late '60s).

One day she wrote her name twice on the whiteboard and asked us to identify the difference between the two; visually they were identical, but she wrote one with her left hand and one with her right. She said as a kid she was made to use her right hand when she started showing signs of left-hand dominance.