Number in the bottom of caster

There is a number punched in the bottom of my caster, RD648752. What does it mean? Does it lower the value? If someone could find out the date of the registered number, it would be most appreciated. The hallmarks are W & H - Anchor - Lion Passant - t.
t should be the date for 1918. Thanks for helping.

The design registration number 648752 was issued in 1915. Its presence does not affect the value. A useful web page describing design registration marks can be found here.

Thank you for your quick answer.

Regards