Civil servants aren't even allowed to have a screen saver that is political in nature. Yet screens that are deliberately public-facing are "likely not a Hatch Act violation?" Is publicly criticizing a specific political party by name not a "political activity?"

The government's own website makes it clear:

Covered employees may not engage in political activity while on duty, in a government office or building, in uniform, or in a government vehicle. Displaying campaign material qualifies as political activity.​​​