I guess the meaning of UTR will differ from lady to lady and how unanimous she/they wish to remain.  
I've met ladies who have maintain a web presence and don't' advertise. Others will advertise and have a no review policy and the most radical would have neither of them.  
In the case of these particular ladies you mentioned in a precious post, they have explicitly ask for privacy, do  not accept reviews and have a web presence  (and some say they were victims of stalkers/harassment).
The fact of sharing her/their information should be asked by her/them, not offered by you, especially not publicly in a place like a board. And even if you share it with a fellow hobbyist, it should be discretely back-channeled.

It is supposed to connote, "NOT VISIBLE to the masses."  If you advertise online, you're not UTR. Simple as that. You might not be "over exposed" or "full time" but you're still able to be booked with one click. Most of the UTR providers I know are not on any ad site, they don't have reviews, nor do most even know what a review is. They book by network and word of mouth.  Some are on P411, but their profiles are set to private and they ONLY see P411 members and communicate via that site.

UTR and Stealth Bombers....

love UTR providers who advertise in the public venue.

This.

Bring your own "plant" we're spitters...lol
Peace & Love

Like almost every other acronym in the hobby, it varies. So just ask the lady or ladies and follow their wishes. When in doubt, follow the instructions. And if you don't know the instructions, just ask.

UTR providers who provide completely offline appreciate clients who understand not to talk about them ONline. So no, you shouldn't post on the boards about a truly UTR lady. If you like to post on the boards about the ladies you see, then UTR gals might not be the route you want to take. These ladies seek real discretion.

I post reviews under a different name but have several years of experience here.  In my opinion, I do think you're being a bit disingenuous.  If the provider has asked that you not to post a review and chooses not to advertise or post on the boards, why not respect that request? Unless you are trying to protect others from a rip-off or potential dangerous situation what is the pus to your posting?  It doesn't seem that this is the case here but simply that you are choosing to publicize people who do not want that publicity.  I think you should simply respect the wishes of the provider.  Providers make those decisions for a variety of personal reasons and I think that you, as a consumer, should respect the wishes of the provider.  If they choose to post on the board, I'm sure that they are capable of doing so.  I simply think that common courtesy should prevail and that their wishes should be respected.

Under the Radar means no reviews (or no new reviews), no advertisements, no web presence, no posting on discussion boards, etc. You may post about her but she probably prefer not. They may or may not appreciate your sharing of her info with friends, but I guess that's the only way she could get new business.