I started using zsh about a year ago after having resisted it with a passion. My main worry was that I would "forget how to bash" and be lost on various servers I log in to. While there are some nifty things I have gotten a little too used to in zsh, I don't think it has been a big problem.
One thing that visually tells me that I am in zsh and not bash is that my zsh terminal syntax highlights as I type. Yes, you read that correctly. If you are not familiar with the zsh-syntax-highlighting prepare to have your mind blown.
When you are typing a command you get a yellow color:
Then when you have typed something that actually is a command you get green:
When you make a typo you get red:
It also makes correctly quoted strings yellow. I find that a nice help too:
On the Github project readme there are instructions for installing the plugin.