These were generally used by ticket agents to imprint the stations on paperwork- tickets, receipts, bills, etc. These two came from a small desktop "tree" that held stamps for many other B&O stations in the mid-Atlantic area, including Washington, DC and Baltimore.
Both the Rockville and Silver Spring stations still exist- the Rockville station is served by MARC and Amtrak trains; the original Silver Spring station is a museum, although MARC commuter trains serve a new facility located down the tracks from the original station.
These two stamps are in a private collection, although they are an accurate representation of the many local history artifacts in our archives - preserving an accurate history of street cars in the Washington DC area comes with the "corequisite" of preserving coinciding local history.