If it's in a concrete ceiling, I'm guessing parking garage or simar. If that's the case, your main concern needs to be avoiding PT cable. If you damage a PT cable, some pretty horrible things can happen. If you're drilling and see colored plastic bits coming out, your day just got really bad. The longer your anchor or fastener, the greater chance you have of hitting PT cable. Some builders won't allow you to drill unless you use a specified length of anchor (often the Hilti I posted) or unless you have the area checked with GP radar prior to drilling.
Those little tiny anchors I posted will easily handle the sign panels you have and should keep you away from PT cable. The allowable loads of those anchors are somewhere around 300 pounds for shear and tension. The ultimate loads are five times the allowable. They're incredibly strong. 7x7 ⅛" aircraft cable is rated for over 1,000 pounds. It's a pretty bulletproof setup I've used on somewhere around a few hundred of these types of signs in parking garages. Zero failures.