Hello! Just a quick question. Is the sh-process logo supposed to look like this?
Someone on another forum told me that this is the logo of Saint Helen (SH) and that it might have been put in there for a joke (or an emoji bug).
I thought it looked a bit suspicious so I wanted to ask you guys!
Looks like the flag for St Helena to me. My wife's parents were both from that island, funnily enough. The island is a British dependency.
@que11, welcome to the forum.
Let me tell you exactly why that flag appears in the System Monitor. I used to be puzzled by it, too.
For some bizarre reason, the default MATE icon theme contains a complete set of pictures of countries' and dependencies' flags. To make it even more bizarre, these flags are stored under the icon theme's animations collection, which I can tell you no country has an animated flag! (I suspect the flags were put here because the FreeDesktop.org icon theming standard [that's a real thing] doesn't specify a standard location where you can put flag pictures, so since the animations directory was otherwise empty, the MATE developers [or maybe the GNOME developers, frankly] put flags in that directory. In ye olde days, the animations directory contained animated spinner icons to show the progress of an on-going process; now there are alternative ways of displaying a progress indicator.)
Anyway, there's a bunch of flag pictures in this animations directory. Check it out yourself: Go to /usr/share/icons/mate/scalable/animations in the file manager and see the over 100 flags in there. Some are huge, because they're massively detailed. (Serbia has a detailed flag, for instance.)
So to cut to the chase: The MATE System Monitor populates the icon part of the process list using a standard function (which is part of GTK, for the developer in you 
). This function looks for an icon with a particular name in the current icon theme, and if that icon could not be found, a fallback icon of the program's choice (in the System Monitor's case, the "executable" icon that appears next to steamwebhelper.sh) is returned instead. The MATE System Monitor passes the name of the program directly to this function. Because this function considers everything in the current icon theme as fair game, the function can return some very unexpected icons for programs which otherwise would have only a generic executable icon, even returning flags sometimes. So for example, running top (a process monitor program similar to the MATE System Monitor) will usually result in an up arrow icon being displayed for the program in the System Monitor. as (a program assembler) gets the flag for American Samoa. And md (a kernel thread for handling stuff like RAID arrays) gets Moldova's flag!
TL;DR: It's a minor bug in the MATE icon theme and in the System Monitor, but nobody's tampered with your system and it's not an "Easter egg" joke.
Side note: It makes one wonder why mate-system-monitor doesn't have a System Monitor icon next to it in your screenshot. On my system it does have an icon next to it. That said, my above commentary still holds true.
Thank you very much for your detailed description! That makes sense (in a way). 
I won't worry about the sh logo anymore then.
However, the mystery of the missing mate-system-monitor icon is now puzzling me 
I double checked on another system running Ubuntu MATE 20.04 and the icon is missing there aswell.
No matter what icon theme i choose it only returns the "generic" icon.