This is a little "home archeology." Our relatively young home was built in 1949 and under the large kitchen add-on we have, there's (at least) two structures: an old porch that was left there stupidly as a support beam and the remnants of an early kitchen floor - two or three levels of it! This tile is from one of those kitchen floor layers.
When we redid the support under our kitchen we found pieces of this tile. I found these outside the side kitchen door the other day, some how having migrated to there.