The Environmental Variable TMSSSLACKICON
specifies the location of an icon to add to the Slack message.
set TMSSSLACKICON=https://a.slack-edge.com/80588/img/icons/app-57.png
$env:TMSSSLACKICON = "https://a.slack-edge.com/80588/img/icons/app-57.png"
export TMSSSLACKICON=https://a.slack-edge.com/80588/img/icons/app-57.png