I don't know either if it has any special meaning, but it's something which is used by
King Records, and you will typically see it on the obi for, at least, their game related releases. There are also similar marks used on the spines of the back insert, early releases looking like
this and later ones like
this.
Organized bootleggers will typically use their own catalog numbering, so always be aware of that when you're unsure of whether an album you want to buy is authentic or not.