Yeah this is definitely something to do with MTP and the Android phone.
Just copying files from the hard disk to the phone. Not every copy, but occasionally one will have that character in it.
Trying it again for quite a while and nothing happened. But then I noticed that the EventTabAddParentname.js.txt (suggested by lxp for my +1 parent in tabs post) here: Consulting - #4 by justin always displays those characters in the tab:
And by strange coincidence, the next file I copied was that js.txt file to the phone, and it displayed the character:
So I don't think I did anything special, just copying the odd file to my phone. I can't say that my experience with copying files to the phone in general has ever been totally flawless (well compared to say, a USB drive).
Maybe S10 is just too old? Phone driver problem? Has MTP been updated recently?
File is definitely there and it all works, it is just cosmetic.