When you read the posts in Moodle forums and you see that somebody has one or many badges, it used to be that when you clicked on (or moused over) one badge, you could see the description of the badge and all the people holding that badge.
This no longer works in the current Moodle site
Hi Germán,
The problem of badges (group pictures) no longer having title tags and links should have been fixed in MDL-65658 when the site was upgraded to Moodle 3.7.1. However, it seems that we still need to make a change in the moodle.org theme (MDLSITE-5814).
Update: Thanks to David Mudrák, MDLSITE-5814 is now resolved and group pictures once again have title tags and link to group pages.