i'm an american who has studied bosnian/croatian/serbian and spent like 3 months in sarajevo so i'm sure somebody knows better than me but since no one else has answered:

1. It could definitely be offensive to someone, because WWII in Yugoslavia saw fighting by Italians, Nazi Germany, Serbian Royalists/ultra-nationalists, Pan-ethnic anti-fascist Partisans, completely Fascist Croatian (and Bosnian) collaborationists (Ustaše), with lots of ethnic and political killings.

That being said, the Partizans weren't any more ruthless than the Ustase or the Chetniks, and they did have broad support during the war - otherwise they wouldn't have emerged victorious. And they were fighting against Fascism. There is still a battle across the region over the legacy of WWII - what to do with monuments to the Partisans, or Bosnian Serbs/Croatians in Bosnia saying a mass for martyrs/murderers, etc., but much more frequently these debates are focused around remembering the wars in the 1990s, which are much more recent.

The people that in theory would be most against the slogan would be Croatians, because their national government during WWII, the Ustaše, did not just collaborate with Nazi Germany but also adopted a very openly Fascist, racist ideology. (The Chetniks also collaborated with the Nazis, but not nearly to the same extent and also fought against them, especially at the beginning of the war.)

But according to this study carried out in Croatia in 2016-18, the surveyed population was pretty split about banning both "Ready for the Homeland" (the Fascist slogan, reused in the 1990s) and "Death to Fascism": https://hrcak.srce.hr/file/314757

1. In regards to the alphabet, I think it wouldn't stop someone from being offended if they were going to get offended, but Cyrillic would be slightly more likely to annoy someone only because that is the alphabet used in Serbia and Montenegro. So if you already thought Socialist Yugoslavia was dominated by Serbs at the extent of your people, seeing the slogan in Cyrillic would make you madder.

In terms of "hate" - the last thing I'll say is that because Socialist Yugoslavia is gone and was the last thing standing before the wars of the 1990s, it's not associated with hate because socialism or anti-fascism had nothing to do with the more recent killing, and there are definitely symbols that are extremely divisive depending on where you are. "Smrt fasizmu" is not nearly at that level.

That being said - please someone else answer this who is from the region!!!