On the site where Hong Kong Park now sits there used to be a large British Army barracks called Victoria Barracks. Some of the old blocks still exist and are being used for other purposes, but blocks A to E that used to be on the hillside have since been demolished and have been used by JC a couple of times. The first time was in Project A, one of the blocks - Block A to be precise - had a false front staircase fitted to it and stood in for the Marine Police HQ. Notice the pattern of the archways, from bottom to top we have a small arch and bigger arch and then a square opening to the upper floor verandah - this design was very specific to the barrack blocks at Victoria Barracks.
It's interesting to note that on both of JC's Project A films (part 1 and 2) neither time has he used the actual Former Marine Police HQ to represent the Marine Police HQ, because in part 2 he used the old barrack buildings over at the Lei Yue Mun holiday camp.
Anyway, in case you are wondering what the building used to look like without the decoration, here is a shot taken from the other end of the parade ground/car park courtesy of the HK Public Records Office.