Slack app on Linux: How to disable the "blue circle" icon on channel activity?

I don't seem to have the setting that Shawn mentions, but i was able to make this work by opening up the /usr/lib/slack/resources/app.asar.unpacked/src/static directory, making a copy of the slack-taskbar-rest.png file and renaming it to slack-taskbar-unread.png to overwrite the version with the blue dot.

of course, that gets rid of the blue dot for all teams, but that's what i wanted.

Edit (2019-05-28): Idea is still correct, but for the newest Slack version (3.4.2) on Ubuntu, two more files have to be replaced. The following worked for me:

cd /usr/lib/slack/resources/app.asar.unpacked/src/static
sudo cp slack-taskbar-rest.ico slack-taskbar-unread.ico
sudo cp slack-taskbar-rest.png slack-taskbar-unread.png
sudo cp slack-taskbar-rest-linux.png slack-taskbar-unread-linux.png

The newest version 4.1.2 doesn't read the .ico file on Linux, and changes src to dist. Instead it builds a badge + base. Luckily unread>0 is the check responsible for the badge and only appears once in the minified JS, so it's easy to patch. You'll need the ASAR tool to modify the Electron archive (npm install -g asar):

mkdir -p ~/tmp/slack
asar extract /usr/lib/slack/resources/app.asar ~/tmp/slack
sed -i 's/unreads>0/unreads<0/g' ~/tmp/slack/dist/main.1.*.js
sudo rm /usr/lib/slack/resources/app.asar
sudo rm -rf /usr/lib/slack/resources/app.asar.unpacked
sudo asar pack ~/tmp/slack /usr/lib/slack/resources/app.asar
sudo mv ~/tmp/slack /usr/lib/slack/resources/app.asar.unpacked

Same idea as notatoad, but with the newest Slack version (3.4.2) on Linux, there are two more files which have to be overwritten to replace the "blue dot" icon by the "rest" icon. I did the following:

cd /usr/lib/slack/resources/app.asar.unpacked/src/static
sudo cp slack-taskbar-rest.ico slack-taskbar-unread.ico
sudo cp slack-taskbar-rest.png slack-taskbar-unread.png
sudo cp slack-taskbar-rest-linux.png slack-taskbar-unread-linux.png

After a restart of Slack, we are rid of the blue dot.