New South Wales 5 Shilling Official Stamp With "O S" Overprint?

Hello to all stamp masters,

can you tell me more about this overprint on this 5 Shilling official stamp?
What does it mean? How does it impact the value?

Thanks!




*** Moved by Staff to a more appropriate forum. ***

Just had a genius thought: Does it mean "Official Service"?

I've heard both "official service" and "on service" but I lean towards the former as more accurate.

Nice example of a difficult stamp!

Why is it a difficult stamp? Hard to find?

(from StampWorld.com)

Yes it's hard to find well centered with full perforations.

The famous philatelist A. F. Bassett Hull explains O.S. as 'On Service' in his 1911 work 'The Postage Stamps, Envelopes, Wrappers, Post Cards and Telegraph Stamps of New South Wales'.

He does so with good reason.

From official Sydney GPO regulations, 1890:

the following is found near the end of the regulations:


Then in 1895 from Joseph Cook of Sydney GPO:


The confusion may arise because O.S. (On Service) is used on official stamps and envelopes.

A good way to remember the correct meaning is to recall O.H.M.S (On His/Her Majesty's Service) without the H.M. in between.

Thanks fairdinkumstamps, you learn something new every day!