Rooting your phone from a normal perspective doesn't change anything. You get a little app in your drawer (the little ninja) and beyond that really that is all you could tell without some sorts of tests, like trying to run something that requires root access.
I kinda like to think of rooting as becoming the manager of a store. The clerk can do all of the basics, but changing prices, doing returns, and some other things a manager may have to handle. Rooting your phone gives you the ability to do things to your phone someone without the permissions couldn't do. Uninstall/delete a system app (corp cal, visual voicemail, facebook...etc), make backups, install custom backups, install kernels and overclock, theme and many many other things.
Now as far as anything done with the rooting, like the above mentioned things, that is rather easy to tell. They may not notice that you don't have facebook, but a different kernel (for overclocking), firmware version, custom recovery, custom boot animation, and a custom theme is rather easy to spot. I am sure there are other things that are obvious too, but I am just saying in general.
So if you were to ever need to take your phone to VZW, taking her back to stock would definitely be in your best interest. I most certainly would take my phone back to stock, as I don't see any reason not to as it isn't a difficult process. You can create backups that save to your sdcard, so that you can be back to where you were before in no time. Just re-root, re-install the custom recovery, and restore your backup.
To check about your phone. On the main screen click the menu button (4 lines between back and home) > settings > about phone (this is all the way at the bottom). Scroll down that page and it will say stuff that changes when you install a custom ROM (usually at least).