Is there a gauge in telling a real woman from a man in a woman's body? Probably not unless she tell you then you will know she's a lesbian.
Is there any tell tale signs she is a lesbian? If we stereotype lesbian then we will picture out a woman who is short haired- probably a barber's cut or military cut, with lots of gel. And perhaps wears a t- shirt with folded sleeves and a matching black wristband and a tattoo somewhere in the arms. But the fact is, unlike homosexual men where there is certain sway and signals to tell them apart from other real men, lesbians now are very hard to decipher from a true woman.
It's hard to distinguish lesbians from a true-blue woman because they usually don't cross dress or act in a 'manly' manner, especially mature tomboys. Today's tomboys are dressed to kill and as hot as any hot chick you see around town. They have manicured nails, waxed legs, great hairs, earrings, and lipsticks. They are gorgeous and there's really no way of telling is they're a 'butch' or not. Maybe the only way to tell the signs she is a 'dyke' is the way she deals and interact with her girlfriends because unlike gays they usually don't shriek and tiptoe. When she is with her friends, especially if she's interested with her friend, she touches her girl friend in an uncommonly conduct, like running her hands at her gf' back in a caressing way, she just love to touch her in a own 'casual' manner.
In order to confirm this, observe her if she does this all her other gf's or even guy friends, if she does, then maybe she is one person who is unaware of her affectionate ways. One of the many signs she is a lesbian is her unnatural reaction when talking about lesbianism- unnatural reaction could mean unusual calmness or erratic reaction like repulsion or hatred. Or she could be very conscious and uncomfortable. They are usually the types who are very defensive and protective about their sexuality. Irrational reaction like this one can usually give them away- with regards to sexuality, there's nothing to be defensive about if she's not hiding anything, right? Though some gay women are so enthusiastic and excited when talking about the topic but this is not a full proof sign she is a lesbian because some people are just as interested when talking about gay women.
Speaking of the way they talk, listen and watch her language and speaking manner with other girls, does she flirt with them in a teasing way? Keenly view her body language and compare it to most girls you know or to other gay women you know- evaluate which category her behavior belongs. Again, this cannot be a defining factor because some women act 'boyish' and some lesbian acts very sexy and feminine. Looking for signs and symbols of gay or lesbian emblems cannot truly tell if she the real thing or not because there are so many straight people who supports their cause.
The only way to know for certain is to ask her straight. She may deny or admit it but whatever her answer is, it will not change her. And it will not matter. Sexuality doesn't measure how good or bad a person you are. Sexuality is not a measurement of your humanity. From the inside, there are no man, women, gay or lesbian- from the inside we are all the same. We all have a soul and our soul has no sexuality.