This issue was created from UI discussions at "Themeing improvements to teaser listings such as "What's going on" Page"
Requesting UI feedback on this.
In a preliminary usability studies we conducted, "plus" icon for following worked better than the shout icon.
The green "on" is similar to Commons' green action buttons used on node teaser for activity stream, for example the attend, comment, answer etc...
Commons Origins UI Design - with Green Action Buttons