The folder icon shows how many documents are required by the lawyers (lawyers office) or how many are being prepared by the legal interns (Legal Intern's Room).
 
If you see a warning symbol on the Legal intern's office, it means that there is no space left for more documents, so it's necessary that the delivery workers take some to free space or you can try to expand the paralegals' office or hire more delivery workers and improve their office so they can be more efficient on their job.