The Choose Site drop down located in the top right of OSM displays the site/s that you can publish OSM messages to.
Below, "Floor 601" is selected and in the main zone playlist to the left of the dashboard displays the messages currently playing at that site.
Note: All messages that have a white background, such as the first seen below, "Holiday Party" were published directly to this site within OSM. See at the bottom of the the main zone playlist, the message, "Promotion" with a light blue background. The blue background let's you know that this message was published at a higher node level within this site's hierarchy.
To see where the message "Promotion", with the blue background is located, go to the drop down and refer to the site hierarchy of where "Floor 601" is located beneath. As seen below, "Training NYC" is a higher node level where messages can be published and the sites below it will inherit the message. Note below how the background of the message is now white, implying that this message was published at the "Training NYC" level.