I'm not sure where I picked up this habit, but I think it might be grammatically incorrect. I'm a fiction writer and have just started working on a new novel, so I want to clear this up before I get too far in. Here's an example, since the question sounds a bit confusing:
The speaker starts off with: "... Shame that...-" Instead of: "... It's a shame that...-" This is how I wrote it: "'Shame that...-"
For some reason, I've picked up the habit of adding an apostrophe at the beginning of an incomplete sentence like that, but I'm not sure if it's just a grammar glitch that my brain contrived randomly or if I saw it used somewhere. Is this incorrect?