When Bruce Willis finishes his Manly Loner dialog in the bar, he finishes his shot of whiskey. Chat, chat. Brandon Lee also hands off his full drink glass to the cop, and announces that the cop will pay the tab; who then sets it down on the bar ... next to a full shot glass of whiskey.
While moving towards the Enemy ship and patrolling the dead alien combatants, Braxton Ryle points his weapon right into the face of Sol Cantos, this is called 'Flagging a Friendly' and is a severe weapons handling violation for any firearm handler. No trained military personnel or even a properly trained civilian would intentionally point their loaded and chambered weapon at another friendly, ever.
A neon sign saying 'Open' can be seen when James Ford exits the bar at the end of the film, but the sign is on the inside of the building as opposed to being on the outside where people can see it.
Early into the movie, the scene where the female sniper is on the ridge, the camera pans from the sniper to Bruce Willis. During this pan, a lot of the crew is clearly visible in the top half of the screen.
In one scene is clearly visible the Earth's Moon, even if the protagonists are on an alien world.