They gave the following details:
I am in the process of getting my PhD. I spend every day doing research. I "do" science. Can I put on my business card, "John Smith, Scientist"? Do I have to wait until I have the PhD in hand? Or until I'm a candidate?
I took a quick crack at it, but I'd love to hear what other people think. Here's my answer in full:
There are two issues here: the first is one of credentials and the second is one of societal interpretation.
"Back off man..."
In the case of credentials, there is no exam, or class, or quiz, or whatever that one needs to pass in order to become a "scientist". There is no "science" credentialing system. Certainly if you are a PhD researcher working at a scientific research facility then you are a scientist. But so are all of that person's subordinates, who may or may not hold a PhD or even a degree at all!
Are Diederik Stapel and Marc Hauser still scientists? They hold PhDs and conducted research, but both were caught falsifying and/or fabricating data. That's certainly not scientific!
The second issue is one of societal interpretation. If you put on your business card "SCIENTIST", that gives the person reading the card the impression that you are currently a practicing researcher or theoretician. If you are not such, then you are being duplicitous and should not "advertise" yourself as a scientist. Not because you're not a scientist, but because you're sending a signal that isn't entirely true.
In your case, you are a PhD student. You are doing research (I presume); therefore you are a scientist.
That said, I believe you'd be better off putting "John Smith / Ph.D. candidate, awesomeology / University of Very Impressive" on your business card, as it is accurate, sends a signal that you're a "dedicated" scientist (i.e., working toward a PhD) and that all will carry the baggage of "being a scientist" for you, without the need to explicitly state it.
Now for my totally biased opinion: just calling yourself a "scientist" (without explicating what field of science you're specializing in) comes across as a little sleazy, like you're taking advantage of a title to pull one over on people. It's like people who constantly refer to themselves as "doctor"...
(image source from an older post of mine)