'Big Time Rush' Star -- POSSIBLE DRONE SIGHTING ... At Secret Service Golf Tourney

What do Secret Service members do when they're not protecting the President ... or boozing in Colombia?? THEY GOLF!!!

And at a recent Secret Service charity golf tournament in L.A., there was definitely some sort of drone keeping watch from the sky.

TMZ Sports has obtained footage showing a fast-moving flying object hovering over the event -- where stars like Kendall Schmidt -- the lead singer from "Big Time Rush" who joined current and past agents on the links at Trump National Golf Club in Rancho Palos Verdes.

We're told the event raised a ton of cash for families of former agents ... including $2,500 from Schmidt, who sponsored the first tee.

As for the U.F.O. ... our sources on the course tell us the drone hovered over the area throughout the day, zipping around the sky. Unclear if was it was keeping watch over the agents ... or just recording the action for fun.