I asked a contact on Flickr who is very knowledgeable about old Baltimore Transit to take a look at this post to see if he knew anything about this streetcar. Here's what he had to say:
This car is actually a steel trailer streetcar from the 1920s. It had no motors or controls. It was pulled behind a regular motorized streetcar. The transit company ran trains of streetcars of up to 3 cars similar to the light rail today. The trailers were quite heavy and were difficult to pull since the streetcars that operated here were not heavy duty enough for them. As a result they were pulled from service in 1932. The car in your photo sat on Reisterstown Rd. for many years and was the home of "Jacks Vegetable Stand". I remember seeing it out there. It now rests in a sad state of deterioration on Falls Rd. at the streetcar museum.