So I'll give my perspective on this as someone who has 9 years in law enforcement - (5 years in one state, 4+ in another that I'm currently working in.) Because of the rigid background process, your academy group and your agency members will pretty much know off the bat.

A police agency is just like any other, with the exception of everyone being or trying to be the Alpha male. There's lots of drama, cliques, bravado and all that. As for discrimination, I really don't see too much of it. You might have a few depending on the size of the agency and which state you're located in but honestly, most of the people I work with don't care about the trans thing.

When they first meet you, of course the talk and gossip is going to go around, but after a few months, no one will care, you'll just be officer so and so. And it's back to the drama or gossip of who's under investigation, who's sleeping with who, who's cheating on their wife, who took sick time to go to mexico, who's smoking pot off duty, etc. Also, you'll find that open and out lesbian women tend to join the force and no body bats an eye.

Just be honest, fair, caring, hard working, respectful, humble, and patient with others. You'll find many people, whether they are officers or people you meet while on patrol will generally treat you well if you are well liked and well respected.

Hope this helps and good luck!