[ajwharton]

Glocks have this feature. I personally don't know of any shooting instructor, combat or otherwise, who teach students to place their index finger on the front of the trigger guard. This includes both the dominant and support hand.

I have been a basic/combat instructor since '91, and I can tell you that is NOT for a finger rest. A solid grip with the offhand index finger wrapped around the grip below the trigger guard is much more effective. The most commonly told story that I have heard is that it is to brace the gun against a forward block, like the chain-links in a fence.

[marktwain]

“I have been a basic/combat instructor since ‘91”

It was fashionable for a while well before ‘91.