Huh, I didn't know it originated at Google. I thought it was just a code review thing.
Is it really a Google reference? Do you have any source for that?
Closest I've got:
> While the story behind the coinage of LGTM remains murky at best, the earliest known use and explanation of the acronym can be traced to a feature summary of Google Mondrian, a peer-review software application for programmers, posted by Niall Kennedy[3] on November 30th, 2006.
"Looks/looking good to me"