The thematic meaning behind the Stop Putin signs matching Ghostbusters signs might be lost on most Americans, but Real Wisconsin News has investigated the similarities in order to analyze the reasoning for the similarities.
To begin, Putin is Russian, and it has been widely documented that Russians are very pale. Ghosts have also been associated with pale/glowing/translucent "skin."
In addition, the ghost's obvious resemblance to a KKK member allows for a similar, racist interpretation of Putin. He is haunting the Ukrainian people, but he is also racist and attacking them because of this racism.
The red is meant to signify communism in both images. Russia, while not officially communist, is still pretty much communist. While ghosts themselves may not have political affiliations, anti-communist sentiment was high in 1980s America, which explains the original movie image.
Another similarity is the positioning of at least one of the hands. Since Putin's other hand was severed in an unfortunate ham-slicing accident, it would not be appropriate for him to have both hands up like the ghost. Putin's hand is also in more of a "Stop, Hammer Time" position rather than a ghost with his hands in the proton pack kind of position, meant to portray Putin as the aggressor rather than the other way around.
The song tie-in also plays a major role in the sign similarities. "Who you gonna call? Ghostbusters!" is the memorable chorus to the original song by Ray Parker Jr. With the new song, also recorded by Ray Parker Jr. and also packaged with a music video featuring B-list celebs, has the lines, "What we gonna do? Stop Putin!"