Legal Question in Business Law in Maryland

If you are doing business in Maryland in a name other than your own, then yes, it needs to be "registered." If you have any sales in this state then you'd need to register for sales/use tax accounts. Most entities need to file annual reports / personal property tax returns regardless of whether they hold inventory.

You're strongly encouraged to meet with a business attorney who can help outline the various legal requirements of doing business in this state and talk about the pros/cons of doing business through an entity (such as an LLC) vs. maintaining a sole proprietorship.