Or it used to be.
I did wonder about the extra / too.
Only thing I can think of is that is was to show it was decimal perhaps?
If I remember rightly 6d became 2 1/2np so maybe it was a "changeover" token as I've never seen a pre-decimal 2 1/2 casino item. I know it was a popular stamp denomination but most of the UK sets of jetons/chips I've seen have 6d, 3d, 1d but not 2 1/2d.
Any other ideas?