I have looked at this topic before in the Cygnet blog (http://www.cygnet.com.hk/blog/how-to-say-no), but it's worthwhile refreshing our thinking about this -- one of the most common examples of 'Hong Kong English' to be found around Hong Kong.
The sign gives examples of 6 prohibited items in Hong Kong, using both pictures and words. The meaning of the sign is clear, but the use of English is non-standard.
This sign is an example of GENERIC REFERENCE: that is, the sign is intended to apply to ALL AND EVERY EXAMPLE of the objects referred to. In standard English, we normally use plural forms of countable nouns to create generic reference. In other words, in standard English, the words for five of the six items on the poster would normally be placed in the plural (the exception is 'Tear Gas', because this is not a countable noun and so cannot be pluralized).
To illustrate the difference between this aspect of Hong Kong English and standard English, have a look at this sign from a UK airport:
Notice that the 4 types of items being discussed are given in the plural (apart from 'technology', which is not a countable noun). They are placed in the plural because these words have generic reference -- that is, the sign is referring to all and every example of liquids, coats, shoes and loose items. What's more, in the lists of examples under each number, all the countable nouns are also given in the plural -- also because they are intended to have generic reference.
You may notice an inconsistency between the way English uses words and pictures for generic reference -- an inconsistency that is not present in Hong Kong! English speakers generally use countable nouns in the plural for generic reference, but they are quite happy to show pictures of just one item for generic reference purposes. In the picture above, for example, List 2 includes 'laptops' and 'tablets' (both plural), but the picture below shows only ONE laptop and ONE tablet. English speakers understand pictures of single items to refer to all examples … but when using words, they expect generic reference to be expressed with plural countable nouns.
In summary: if you are using a countable noun to express generic reference, make it plural.
About this blog
This blog arises from keeping an eye on English in Hong Kong. I often use signs, notices and advertisements that I see as starting points to write about English issues that commonly challenge Hong Kong writers.