It was a short way of writing a different spelling of the words all correct. Some foreign-born people wrote all correct as o-l-l k-o-r-r-e-c-t, and used the letters O.K.

VOA: special.2010.02.28

The address is u-s-a-l-e-a-r-n-s dot o-r-g.

VOA: special.2009.01.15

"His name is John Barovetto, B-a-r-o-v-e-t-t-o.

VOA: standard.2010.05.31