Quite an obscure one I admit, but let me explain.
In the latest episode Ponyville is shown with what can only be described as an air raid siren. This got me thinking as to what it is actually used for, and thus the idea of a World War style poster came into fruition.
Picture of the original poster [link]
Couldn't find any large images of it.
I wasn't certain on who to include on either side, so I ended up just going for some of the more memorable ones. (Yeah, I know Gilda isn't friendly per say, but the Griffin race probably is in relation to ponies.)
Now for a buck ton of vector credits.
I think that's all of them, I might of missed some. There all in my favorites if you want to check them out.