I've looked at that stone plaque many times. It consists of a crown and I think the date is 1901. I think it's nothing more than a nice bit of decorative architecture, commemorating the date the house was built. It was plain sandstone, until someone decided to paint it white a few years ago, which I think is a shame.
There are stone images of Queen Victoria on the side of houses at the junction of Sidney/Gonville and Cambridge Roads, again with the date the houses were constructed. I don't think many people know these images are there, as you have to really look up to see them.
A lot of buildings in Bootle are like that, you have to look up see see the interesting architecture/stonework.