Visible crew/equipment: While Aunt Bee, Andy, Barney, and Gomer are on the porch talking about the band, just as Andy says, "We're talking about gettin' up a band concert by tonight," the chalk T-mark is visible on the floor by Andy's feet. (00:12:25)
Visible crew/equipment: Barney shows up with the concert sign while Andy's sawing wood, and when he and Andy talk about it, the shadow of the boom pole/mic is moving around on the ground, at the lower left corner of the screen. More of the boom's shadow is visible again, when Gomer shows up and they talk about Goober. (00:14:30)
Visible crew/equipment: At the end, when Dr. Breen tells the very tired group, "You all look as serene and relaxed as if you'd just finished listening to a pleasant band concert," in the next shot facing the porch, the shadow of the boom mic is moving around between the two windows above Clara and Andy, at the top of the screen.
Answer: As noted in the previous answers, in real life, things like this provided wind and/or rain deflection, and also maintained a bit of privacy when blinds were raised somewhat. The interior courthouse set was located in the studio, so the "outside" Main Street didn't exist. I believe these things were added to the courthouse windows for practicality, to avoid some crew movement being visible on the opposite side of those windows. These are not "window boxes" to hold anything, as they're actually bottomless; we can see the Venetian blind's long pull cords under them. They're made of plywood and simple to build, so the "material and labor" was inexpensive. Similar variations made of different materials are in other movies/shows. In 1957's "12 Angry Men," textured chicken wire glass panels are in the jury room windows, and in "Jesse Stone: Night Passage" another type is in Jesse's office windows.
Super Grover ★