I need to make a sign that is rain and snow-proof. This will be put in front of my house for a while during winter (it is usually well below -20C here, sometimes even -40C). I don't expect this sign to last very long in this weather so I will most likely be taking care of it every few months when the ground becomes unfrozen.
You can see the general shape in the sketch below. There is a frame which I will make out of 2x4s an you can also see the two glass panes that will be "sandwiching" a paper sign on one side, some black cardboard, and another sign facing the other direction.
What you don't see in the sketch is the glass' frame which is the part that I'm stuck on. I need to make it so that I can change the sign frequently and also make it waterproof.
My question is what can I do design-wise in order to keep water out of the paper sign and at the same time be able to change the sign every now and then?
Consider that I have almost every woodworking tool available to me (no CNC though) and I have to whip this out in 5 days so that it can be ready for Halloween which is when the most people will see it. I can have a "beta" version for that day and go back and tweak it later.