cs (Chinese-style sentence)
This mark means that this sentence is structured like a Chinese sentence, rather than an English sentence.
At a basic level, English and Chinese sentences are structured very differently. I like to think about the differences this way:
English sentences are like a tree, with many clauses branching off of the main trunk.
Chinese sentences are like bamboo, a series of segments one after the other:
Notice how each of those five clauses is a complete sentence on its own. You could just as easily use periods instead of commas:
Now imagine you take that bamboo sentence and translate it directly into English. It would look like this:
Chinese sentences are like bamboo, their structure is simple, the sentence's stem is made up of segments, there are no branches, it's not hard to write.
This is a very unnatural sentence in English. The reason it seems so strange is that it is missing coordinating conjunctions. In brief, a coordinating conjunction introduces another clause that is a full, grammatically complete sentence. Here is one way that sentence might look in more natural English:
Chinese sentences are like bamboo. Their structure is simple, because they are made of segments and do not have branches, and so they are not hard to write.
In this sentence, "because" and "and so" function as coordinating conjunctions.
If you see the "cs" mark on your paper, ask yourself: How could I include coordinating conjunctions so that this sentence sounds more natural in English?
In addition, consider splitting the sentence into shorter pieces. A "Chinese-style sentence" translated into English is also often a run-on sentence -- a sentence that feels much, much too long!