General rule of thumb for spoilers:
If it hasn't been posted to the movie's official web page (
http://www.godzillamovie.com/) then it's a spoiler.
Obviously, there's some leeway there, especially with regards to anything that could be considered speculation. If you're speculating, it's clearly not a spoiler.
If you're second-guessing whether something is a spoiler or not, then it is. If it reveals part of the film's plot, then it's a spoiler.
A half-second of thought is all it takes to not ruin the experience for others. Some people would like to discuss the film, speculation, pieces of concept art, trailers, official still, etc without having to worry about character fates being revealed.
If you're unsure, put spoiler tags on it; and if you're really unsure, there's a whole separate thread for spoilers, feel free to post there for the duration of the lead-up to release, I don't care.
Use a little common sense and a little common courtesy.