What doesn't J-20 have a nickname printed on its body, but J-31 does? It seems to me that the J-20's PLA star looks more professional. Is Shenyang trying to be cool?
IMO the J-20 is an official PLA-founded project, whereas this type - J-31 or whatever it is called - is simply like the FC-1 an export-related type. Have we ever seen a FC-1 with a PLA/PLAAF-symbol on it ?