This depends on contexts. But a couple I've noticed:

- Way, way over the top "girly" writing with a bunch of emojis and hehehe stuff.

- In a sexual context, constantly posting on misogynistic stuff and being like "oh god I wish this was meeeeee"

Editing to add the funniest thing to me: in certain forums, there will be someone who posts a ton of pics (of someone they claim to be), they are super open and down for anything etc., but the second you ask for actual proof that it's them (something simple like a quick selfie holding a custom note) there are a thousand excuses. It's the combination of these things that is so funny. A woman posting herself all over the internet WOULD be willing to provide that kind of proof.