The official Instagram has posted the picture as well:
https://www.instagram.com/p/BMRVFMhh-M8/
If no announcement comes of this, I'll be very surprised. I don't think this is a "Hey casual fans, Dangerous is turning 25!" kind of thing, it's intentionally a simple image and title, I think they want to start the hype.
EDIT: Just noticed the post on Facebook: "
All this month, we’ll be celebrating the 25th anniversary of the release of Dangerous!"
Not a good sign, very odd decision to update all of the social account cover photos to "Dangerous 25" for a month-long casual Dangerous promotion, especially knowing that "Dangerous 25" has the same name format to "Bad 25", something that was actually released. Casual and hardcore fans alike could easily get confused seeing that on social media.