It is common practice in shuls around the world for congregants to hold their pinky finger up to the Torah when it is opened and lifted for hagbah. Interestingly enough, however, the source for such a practice is far from clear.
The earliest mention of such a practice is Me’am Loez on Parshas Ki Savo, 27:26:
“It is customary to point to the writing with the little finger and to kiss it.”
There is no explanation, nor any other background given to the practice. Indeed, Me’am Loez is a Sephardic source, and, as such, Ashkenazim don’t really even have a source that it was ever something that was done at all.
There are sources here and there that state pointing at the Torah during hagbah could be a good thing to do — as you say “zos haTorah…”/“this is the Torah…” — but nowhere do these sources suggest that it should be done with the pinky finger. After all, who points at something with the pinky?
What is really interesting is that the origin of the practice is completely unknown. The Me’am Loez simply records a custom that he observed. There is no known origin for the practice. It seems as if it is yet another one of those things that slowly caught on, and snowballed over time.
In fact, if you were to ask someone why he or she points with the pinky during hagbah, the answer will most likely be something along the lines of: “That’s what I’ve always seen everyone else do.” This isn’t a minhag that is even taught. It is almost always picked up simply from watching what other people do — which is probably how it somehow got started way back when as well. I'm legitimately curious.
Of course, it’s not a bad practice, per se; it’s just odd. If the goal is to point at the Torah, nobody does that with a pinky. And if the goal is something else entirely, it is utterly unclear what that goal is, and if it was really the impetus for the custom, or merely invented retroactively. (It is also reportedly the case that both Rav Shlomo Zalman Auerbach z"l, as well as Rav Yosef Shalom Elyashiv z"l were opposed to the practice — although I do not have a clear source to support this.)
During hagbah, just stand up, make sure you can see the words written on the parchment, and then say the posuk “vzos haTorah…”. That’s the halacha. If you’d like to point during this ordeal — using any finger — by all means. Which is to say, I don’t advocate to stop the practice; I just don’t see any reason why anyone would do it.