Responses
No, is a normal T-shirt, That image has been used and used over and over again. For a moment it was even a meme. Just googled in [google images] "keep calm and carry on" and you'll see the repetitiveness, haha.
I did it for you, here it is: https://www.google.com.mx/search?q=keep+calm+and+carry+on&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiMmL68majXAhWB4CYKHfABDiwQ_AUICigB&biw=1440&bih=755
Isn't the t-shirt worn by Ah Shang in this page a reference to a book, "fangirl"? http://www.mangago.zone/read-manga/circle_wang_zi_ying/mf/362bbe216013480a/Ch52/pg-2/