Leeward Islands Scott#2, Sg#2 With Purple O.b. / 10 Jun 99 Cancel

I was wondering if anyone could tell me about the cancel on this stamp from the Leeward Islands.

Does O.B. stand for Official Business, as it does on Phillippines stamps? So maybe an Official stamp "forerunner" of sorts? Or is it a revenue cancel of some type?

With the color catching my eye, and the box of the cancel matching the height of the stamp very closely, I was curious. I don't know much about the cancels of this era of the Leeward Islands, so would appreciate any insight!

Guess:
Revenue cancellation.
Not a postmark.

It is definitely a revenue/fiscal usage. Nice one. Note that British empire/Commonwealth stamps are marked "postage & revenue" so can be used either way. Even ones marked "postage" only like the British Seahorses have been used for revenue purposes.

Hopefully, someone can interpret "O.B." Since the frame extends upward, "O.B." may be only part of the story.

Possibly part of the name of the company or institution that cancelled the stamp.

looks like a bank receipt marking