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

By 1852-53,Boston and New York think about this--Boston-- although we're getting close to that again Boston and New York had 50% foreign-born populations.

在1852年到1853年间,波士顿和纽约,你们听听这个数据,虽然我们现在又快接近这个比例了,那时移民占据波士顿和纽约人口的50%

耶鲁公开课 - 美国内战与重建课程节选

For foreign-born Americans, it supported their right to full citizenship.

VOA: special.2009.07.09