ajohn

A5 is an interesting bird. It was first trapped on Pond #11 at Mai Po in January 2011, and remained there through March 2011, preferring to stay on the gei wai rather than in the bay with most other Avocets. It was seen again on Pond #16/17 in May 2011.
It turned up again on Pond #11 in February 2012 and has been seen there a few times since, again apparently preferring the gei wai to the bay.

As Katherine mentions, the two=-flag combination is essential to demonstrate that the bird was flagged in Hong Kong. We have had many overseas resightings of waders which can be recognised as HK birds by the white over yellow combination. We choose to use engraved flags for both colours partly because this allows the combination to be recognised even when one flag cannot be read (not an unusual occurrence).

ajohn

It's a common problem in Hong Kong. The HK flags are easily stained. This seems to happen more often on birds using the gei wai or freshwater habitats - Wood and Green Sandpipers are particularly prone.
The flags are often interpreted to be yellow-yellow or yellow-orange and observers need to be fairly careful not to assume they are birds from elsewhere on the flyway. When familiar, the stained HK flags are obviously different from orange flags. If in doubt, posting a photo would help.