Security signs usually make me laugh. They're so earnest and serious and I can imagine them being discussed and approved by a committee somewhere. I suppose that people may see signs reminding them to abide by security procedures for the few weeks that it takes for them to have the security procedures ingrained. Then they completely stop seeing the signs.
This one amused me more than usual. It's a good sign, really, drawing on the psychology of the stop sign, and it's trying to come up with a catchy acronym for the security area. But while SIDA is something you can catch, well-displayed security badges are not the usual prophylactic technique. I believe SIDA is also the Spanish acronym, so perhaps the reference is deliberate, rather than having been conceived in monolingual innocence.
The one below was repeated at about eight metre intervals all along the fence of the Salt Lake City ARTCC. They wanted to be very sure that even casual invaders with poor peripheral vision understood about the threat to human life that their invasion proposed. The facility behind the fence shared an architectural style with my highschool, and probably every other institutional building constructed in the 1960s, but it was in good repair. I guess the signs, and the absence of teenage hordes, kept decay at bay.
And I have no idea what the "flying colors" forbidden on this one are. It must be a gang thing. I didn't go in there.