Brettski, I use simple "No Trespassing" signs DIYd by spraypainting through a stencil onto aluminum and vinyl siding remnants. IMHO you want to keep the signs simple. Don't post "no" for activities which you do - this invalidates the notice, if not legally at least in people's minds. For example, don't post "No Fishing" at a pond you fish on. After this was pointed out to me, I removed my "No Trespassing - No Hunting" signs as I do the latter activity all the time.
I strongly suspect Illinois law states how close together No Trespassing sign have to be wrt liability.
Go ahead and get that PLUP (Personal Liability Umbrella Policy). Ours ($3M) is the cheapest insurance policy we have, and potentially the most valuable.
Ohio law is that children below a certain age (10 or 13, can't remember off the top of my head) are NOT responsible for their actions - if they get hurt on your property it's your problem. Yeah, I think that sucks.
If you are on your property during deer season and there is hunting around you, I strongly recommend you wear dayglow orange when in the woods. No, you shouldn't have to, but it's like seat belts - you don't plan on having an accident. Yeah, I think that sucks, too.