Here’s what happened to a trans person that I know:
She lived in a small town on the outskirts of a major Southern city. She posted an ad on a personals website. She included pictures and a description, like most other ads, and also mentioned that she was trans. She didn’t hide this.
She went on a handful of dates over a few months. One guy clicked, and they had an intimate encounter (let’s call it 2nd base, or something like that). They lost contact – she figured he’d lost interest. Then, out of the blue, about a month later, this guy (a spammer who was almost certainly him, based on some of the details of the incident) emailed/posted on social media to her boss, many of her family members, friends, and neighbors, with pictures (the same picture from the dating site), that she was a lying dirty trans expletive. Not all of her friends/family and none of her coworkers were aware of this. It became unbearable and she quit her job.
In my understanding, this kind of thing is not a terribly uncommon experience for trans folks who openly date online. Many of them are probably already out, so such an outing is irrelevant. But many are not. Outing one’s self carries considerable risk, and thus many trans folks will opt to “save” such information for when it’s really, really necessary – i.e. before an intimate encounter with someone they believe they can trust. There’s a risk there, of course, but that can be minimized by timing the conversation to a public place – like at the end of a meal at a restaurant.
In a society (or maybe just a locality) with lots of transphobes, some of whom are capable of violence, there’s no 100% safe way for trans folks to date. Based on conversations with trans folks, I think the safest strategy is to reveal this information in a public place after some level of trust and rapport has developed, but before any intimate encounter.