I've spotted a few MD 1 shields (mistakes) in Baltimore along US 1. They look rather new and all part of a common batch of signs, but I rarely use US 1, so I don't know if they are a recent addition or if they are a year old.
You can find them on US 1 SB just south of North Ave. and on US 1 NB just east of MD 372. There are probably more. None had a direction banner with them. They don't exactly match the standard SHA version of the MD shield but are designed to look similar.
I have not spotted any new US 1 shields. Any US 1 shields I've seen have been there for many years.
I've only seen one, and it was the SB one. http://www.alpsroads.net/roads/md/us_1/smd.jpg
Saw the MD 1 shield east of MD 372 last year, seemed almost new. Sounds like the other one would be up on Fulton Ave. Baltimore City does its own maintenance and signage, so you get more of a variety of styles than out in the counties.
There was a new US 1 shield at the eastern end of Washington Blvd., off Russell St adjacent to Camden Yards. No directional signage; Washington Blvd. doesn't become Alt 1 until Monroe St, and main US 1 until Southwestern Blvd. across the line in Baltimore County.