If you were pretending however, who could say that not other people were into it as well? If someone had the intention to troll, they could simply have other people of both sexes around who could hold the paper. There's no guarantee either way in the end. Especially with AI art nowadays there might be more and more ways to fool people. The promt "a female holding up a paper saying 'word' and 'current date'." could easily be used to create exactly what you might want or expect to see.
My point is, there's no guarantee either way that you might not fall for a fake in the end.
The insinuation is, that I doubt this method of "authentication" would be of any relevance apart from this kind of meetups. Why would you need this authentication when using the forum in the way it's intended to be used. Do I have to hold a paper up into a camera to be allowed to respond? Why would that matter? That's my point.
Some guys can have pretty feminine hands. Both sexes can have long fingernails. Given, you're less likely to find them on most guys, but if someone wanted to fool you, anybody could buy fake fingernails and glue them on. Not a proof either.
Doxing, also doxxing is the action or process of searching for and publishing private or identifying information about a particular individual on the internet, typically with malicious intent.
While dox(x)ing one self would be to willfully giving out those information to other, probably hostile parties.
I can only assume that you're mainly interested in sexual conversation and don't want them to be with a person of your own sex, otherwise I can't see why you were so insistent on identification. And if this was the case, then sadly I can't give any advice. On the internet, most women are men. Old wisdom of the web, still rings true today. There is no guarantee that you wouldn't or couldn't be deceived. You certainly should remain skeptical. But if you don't intend to ever meet the other party, then maybe just assume they're the person they're telling you to be. If you never meet anyway, their true identity wouldn't really matter, would it?