Number 1 is incorrect. The Gunsight Academy sign chezuki posted is correct.
To say, "Treat every gun AS IF it is loaded.", is a softening of the language, and implies that there are times when a gun is unloaded. Too many people have been shot by "unloaded" guns. It is far safer to operate under the premise that every firearm IS loaded.
That's just dumb. It's like saying "give 110%" - it's impossible and there would be no ammunition shortage if it was possible. Also, I'd never be able to take a gun to a gun show to sell - I'd never be able to comply with the "unload all guns" sign!
People have been shot because they treated a loaded gun as if it was unloaded. If you follow the converse and treat an unloaded gun as it was loaded, no one gets hurt. In fact, to say "operate under the premise" means to indeed "treat as if loaded". To say "every gun is loaded" is just plain delusional or dishonest.
It's totally possible to unload a firearm and then PROVE that it is unloaded. We go through this drill when we store firearms or clean them.
I'll gladly accept any insult about be a grammar nazi.