Before bits and pieces of Google+ departed from Google's web toolbar earlier this month, the bar's notification panel began labeling notifications according to their origin. G+ notifications for example got a Google+ icon, while notifications about a user's photo library got the Google Photos badge.
Tonight it looks like Google is rolling out another change to the panel, adding a settings button which allows users to filter out G+, Photos, or YouTube notifications individually.
Interestingly, not all sources appear for all users - it's unclear exactly how the panel knows which options to show, but it appears that the presence of Photos or YouTube options partially depends on whether you've opted to receive those notifications in the Google+ settings. Blogger is also included in the "Post" notification settings on Google+, but - to our knowledge - it hasn't made an appearance in the panel yet.
Whether, as some have speculated, Google plans to expand the "Google notifications" panel even further to include more of its web properties remains to be seen (fingers crossed), but this filtering mechanism would certainly make such an expansion a little easier to handle on the fly.