A script is not supposed to contain images, so you can't include one. Use the description you have, without revealing it is Chinese, and later reveal the source.
Anybody considering your screenplay is going to read 100% of it ten times before they commit any resources [other than their reading time] to it, so NOT revealing it immediately will not be an issue.
If and when the script is produced, the director will know the nature of the writing and get an artist (and perhaps native chinese writer) to produce the drawing correctly in the early scene.
The problem I see with this plot line is that anybody that reads Chinese (like four of my personal friends) will know immediately what the writing is on screen, and that may ruin the movie for them. Or for people like me (I don't speak, read or write Chinese), I might find it ludicrously implausible that none of the main characters are world-savvy enough to recognize your 'puzzling symbol' as Chinese (or at least oriental) writing for half an hour of screen time!
You might be better off making it a more obscure pictorial writing. (I know there are others, I don't recall their names, but you could do some research.)
Added: You could look into Dongba Symbols for the Naxi language, an independent development of script from Chinese characters. It is written left to right (like ours) but if written top to bottom a reader would still understand it, just as we understand vertical English text. This is unknown enough to not be recognized by most Chinese, I would think.