Thank you,John.
With the information you provided, I concurred that what I saw this morning at Nam Sang Wai with a Hong Kong flag E4 was a Common Greenshank, as I doubted at the moment I saw it whether it was a Common Greenshank or Marsh Sandpiper, as it has none of the outstanding characteristics of the other species you mentioned.
By the way, are there any specific meaning with the fist alphabet and the following numeric of the engraved leg flag? I am immensely love to know more about bird watching as I am green in it, and I really mean it. I started birding watching only since February 2012. So far I watched 22 times with 17 of which on waders, as it is only a 20 minutes bicycle ride from my home to Nam Sang Wai.
Please advise.