Using Linux (Fedora, specifically) as my primary workstation, I noticed, at times, strange non-printable characters like in the following screenshots (bottom-left in the first image and upper-left in the second image):
In the image above, the non-printable characters appeared in gnome-terminal with bash shell. I was quitting from ipython interactive shell by a
In the image above, the character appeared in a webpage opened in firefox, specifically RFC 822 text file, just before the table of contents of this RFC.
I'm curious and want to know what they are. I infer that these are some sort of representation of Unicode. Am I right? If so, where is this kind of notation defined? What is it called?