The Status feature in Remote Desktop Manager will allow you to create pop-up messages to communicate information to users when launching sessions. The message will also display at the bottom of the dashboard when the entry is in focus like this:
Right-click on the entry in your Navigation pane.
Go to Edit - Status - Edit Message.
Enter the message you wish to display in the Message section and click OK. When the connection is launched, it will show the message you have entered.