Owing that the penis may not make the best lie detector, suppose this is manual stimulation of a woman with the fingers. Are there tell-tale signs, apart from sounds, such as certain muscle contractions, that would allow one to determine if it was a real orgasm? What and where? If she was well aware of her anatomy, how well could a woman learn to fake these signs?
There is a flushing of the skin on the chest, although this might not always be obvious.
A real orgasm, when held up to a strong light, will have a faint watermark, usually a picture of one of the US Presidents.
How to spot a fake orgasm
Well, the ones the street vendors have are always fake.
Seriously, aside from some flushing (which will be hard to spot, especially in the dark) I don’t think there is any way to prove whether an orgasm is real if the woman is determined to get one past you.
You would never know.
You are SO right. 
But, to address the OP. First, I’d like to say, we are all responsible for our own orgasm.
If you are concerned about pleasing her, then ask her if what you do makes her happy. Ask her what you could do differently to increase her pleasure. If she gets out books and diagrams, perhaps she’s been faking.
Honest communication is the only way to know for sure.
Also, if you rub them between your thumb and fingers, there’s a distinct texture which is lacking in fake ones.
President Johnson?
This is a test with (IMHO) no false positives but many false negatives:
Vaginal contractions. Note any rhythmic or sudden tightening, almost spasm like. Also female ejaculation, another pretty proof-positive sign.
Simple tightening often preceeds an orgasm and isn’t really proof of a real orgasm.
Unfortauntely, a large portion of women won’t show this “sign.” Or maybe they were never really getting off with me and just lying.
Who knows for sure? No one.
But who cares? (I keed, I keed)
Anyway, the best solution for your particular questions relating to whether or not your lover is climaxing with you is probably to just ask her. Honest communication isn’t likely to hurt.
Or just shine a 1800 watt xenon-halide lamp through her and look for the watermarks like 1181 suggested. Pretty funny, by the way.
Johnson or Bush.
That made my day!
When she’s reading, a real orgasm will make her lose her place. 
Why would anyone want to fake an orgasm?
Who cares? As long as YOU had an orgasm, that’s all that matters.
“I want what she’s having!”
Ah, Grasshopper, you have much to learn!
A well-satisfied lady is far more likely to wish to repeat the pleasure with you. Again and again…
…and the ink rubs off
(My bold)
“female ejaculation” is simply a bit urine expelled during sex. All I can say about the “rhythmic or sudden tightening” is, practice makes perfect. Men are so gulible, sometimes.