Revealed in personal ads
The advantage of doing so is that you can weed out people who are unfamiliar with transgender people, which also means you can be on a trans date without being asked some annoying questions. Another advantage is that you can attract people who are attracted to your gender identity. The downside is that it may appeal to people who don't respect transgender people. If you're uncomfortable with the language someone USES in an email, tell them or ignore them.
Revealed in the e-mail or chat
You can choose to respond to people's ads, or to leak your information in chats and emails. Remember that you have the advantage of starting the conversation at least before you meet, and if the other person is negative, you don't have to deal with them face to face. One of your hidden downsides is that if someone responds negatively, they may repost your email or disclose your personal information online, or otherwise violate your privacy. This is why anonymous email accounts are created.
Disclose in a phone call
Disclosure of your information in this way is less likely to violate privacy or public information if someone responds negatively. In addition, it is helpful to be able to hear the tone of the other person and to know their language usage in a timely manner. Email and chat are easy to fake and less real. Phone calls can give you a more realistic idea of how sensitive and knowledgeable a person is about transgender dating.
Revealed during the date
Dating is an ideal time to talk about gender identity, as it is likely to be about your life, work, background, family, etc. But if someone's reaction makes you uncomfortable, you'll bring it up in public. Again, it can be presented in the context of discussing safe sex, or in your context.
Disclosed in sexual contact
Some people choose to talk about it in terms of sexual safety or gender identity. That may make people feel that there is too much or no chance to discuss it in advance. By this time you know you want sexual contact. One potential downside, however, is that if the person responds to you in a threatening way, you may not be in the public eye. In addition, sexual conversations can be awkward if they are raised in non-sexual environments such as public place. Sometimes it can be more difficult to discuss sex after sex has begun.
These are safety tools that can be useful to some people in some situations. You will never be responsible for the actions of others, so if you follow some of the tips mentioned above and still can't prevent attacks then you won't be blamed.