1) When a woman comes in to the ER at 3AM requesting an STD exam and/or a preganancy test, she may be an idiot, or she may be nerving herself up to tell you she's been raped.
2) When one partner comes in with "slipped in the shower" injuries, and the other partner is hyper-protective and demanding in a "why aren't you making my precious baby all better and fixing all her pain RIGHT NOW" way, this is a very good indicator that they did not slip in the shower. (Even moreso when the injured person herself is all "no, really I'm okay and it doesn't hurt that bad, I'm sorry he's bothering you" about it.)
3) When I know he hit you, and the nurses all know it, and the doctor knows it, and the cops know it, and the janitor knows it... isn't a damn thing we can do to help if you stick to your story about that dang slippery shower. I understand why victims cover for their abusers, the myriad of both psychological and practical reasons. I understand that you may feel that telling this lie is necessary for your survival--and I even understand that you may be right. But it still drives me INSANE.