As someone who used to do a lot of drywall (I have a checkered past ) The plasma TV can be replaced and insurance might pay for it, an old and possibly rare sign, perhaps not. If you do go into drywall, do what they do at galleries for heavier pieces, use two hooks.

There are lots of ways to have drywall but set up a system where you still are anchored into wood. Like having a small piece of plywood screwed into studs that the sign would cover and be attached to.

I inherited a European hanging bookshelf system where the shelves were metric, so when we did the house rebuild after the tornado, I had wood put in at all the screw heights between the 16" spaced studs--just like some of the better home builders do for their towel racks, etc. My books would bow the wooden shelves but the verneered but metal vertical pieces the brackets were on, never budged. Plus I hit wood no matter where I placed the bookshelves left or right on that wall.

I have sheetrocked walls in my garage and I put brick panelling on it and that is probably only 1/4" thick, I glued it on and used paneling nails into the studs and I have had no problem with it holding large signs. I have a 36"x72" Porcelain sign that has been hanging on it for 6 months.

1/4" plywood would be fine, 3/8's is better. Ensure the plywood is secured to the wall studs and not the drywall.

Alex the signs are going to be sitting flush against the plywood (vertical to the wall) therefore the screws are holding the sign flush against the wall. Would take a tremendous amount of force to cause the screws to pull out of the plywood (use screws with coarse wood threads). The downward force of the weight is perpendicular to the screw shank.

Different then if the signs were being mounted perpendicular to say a ceiling where the sign is suspended and a greater load/force is exerted on the screws. In this scenario the screws will eventually pull out because the downward force of the weight is linear to the screw threads.

Clear as mud. Hopefully, I articulated it well enough for you to visualize what I was trying to explain.

That's a lot of Big Words Dave!! LOL!!!

It was the only way I could explain what I was visualizing in my mind. I think my mind is like my shop; very cluttered.

Jason, Dave & I live on the Edge of The Ring Of Fire {Earthquake Country}.

tear what you have down- insert 2x6's in wall anywhere you will be hanging big signs, clocks etc, take pictures so you remember where there at. you might want to insulate outside walls- drywall with 3/8" drywall- anchors in drywall hold signs well..

What's wrong with just using wallboard anchors? Each one holds 50 lbs.

Don't cover up sheetrock with plywood, especially OSB. You are covering up a great fire stop with a wonderfully flammable wood chip & resin fire trap. For the mamma-jamma size signs, screw 1"x3"s to the studs, paint to match your wall & be done with it. I have seen too many shop's/garages destroyed by fire where large amounts of OSB was present, where sheetrock would have stopped the spread. (I am not a sheetrock salesman, I am a firechief). As a matter of fact, our flashover simulator for the new firefighters is powered by 3 sheets of 4x8 OSB & half a bale of straw.

Here is an option that has worked well for me.Remember,at the top of that stud wallis a double thick plate;probably doubled 2X4's or 2X6's stacked for a thickness of 3" with a seam at 1&1/2 ".I took a 1/4" eye lag screw long enough th go through the sheetrock and on up through one level of the plate and on into the second piece.I drilled a pilot hole,at an angle to minimize verticle load and eliminate any possibility od hitting the seam,and screwed the eye lag in.

Then using master chain links I simply hung my 42" Texaco at the desired height.I didn't bother with any other screws attaching the sign to the wall.The top sticks out from the wall about 1" but that doesn't bother me;no more holes in thwe wall.I t has been there for years.

If you like,you could anchor it to yhe wall in a few spots using anchors as shown.Good luck.