Noob alert! Remember to put on your kid gloves! Seriously?
I don't like this at all. Yes, some people are new to the site. Yes, we should know that they may not understand all the rules. But no, we should not stick a big noob warning on their profile tag for everyone to see. Not only does it feel slightly passive aggressive, it automatically puts people into the mindset that the "new contributor" will not understand how the site works, or even the concepts behind the questions they are asking.
As an anecdote, I've had maybe 10 accounts here over the years, some anonymous or unregistered. This one is the one I've kept for longest. I still occasionally post anonymously for various reasons. I have noticed a troubling trend. Whenever I ask from a new account, the answers I get are often dumbed down or explain things I already know. This happens even if I am showing a clear understanding of the concepts I am discussing. If I ask the question on my main account, I notice that the answers are far more technical and helpful. The only possible reason for this is that people are looking at my rep and assuming I am naïve. This would be made much worse if people were given a big notice that I am a delicate new user...
We should not judge how new someone is by their time on the site, but only by the quality of their contributions. If someone is using the wrong tag, that is when you gently correct them. If someone is asking a question in the wrong place, that is when you point them to where they should go. Unless someone is showing that they misunderstand the site, we should treat them as equals who are equally competent (and who very well may be, as many people who are writing their first question have been reading Stack Exchange sites for years). The idea that we are putting a big noob alert on people's profiles is disgusting.