It's not just on criminal or tactical matters that we can betray ourselves. More than once, I'd end up rolling to do some supervisorial intervention on a pissed off citizen. The beef? The citizen heard an on-scene traffic deputy identify the party at fault. They will find out soon enough who's at fault once the report is processed. Besides, you may find additional information once you're well away from the accident scene (such as verification that traffic signals were not working).
If you see a dirtbag, act casual as though you never even noticed him. Check out the skirt on the sidewalk instead. Then slowly work your way into a position where you can catch up to him.
Plan on camouflaging your motives, too. Once, I spotted a guy loitering by a mailbox. Because of the configuration of the roadway, I was able to see his torso just as he picked up on my lightbar. Neither of us saw the other's face until I made the bend in the road. By then, he'd opened the mailbox and tossed something inside. I happened to know the residents of the house—a finer bunch of dope-dealing fiends you couldn't hope to meet—and knew that this guy wasn't one of them.
I pulled up on the pretense of wanting to speak with someone inside the house, and inveigled him into the backseat of my patrol car to wait. I then checked out the mailbox (PC: tampering with U.S. mail) and found a bottle of rock cocaine inside. 10-15…oops….another run rides the bus (that personal code thing).
Finally, remember that once the guy is locked up, it isn't the end of the game. You may have to appear in court. If you end up having to refresh your memory, make sure you're not going over notes and reports with the D.A. in the hallway and saying things like, "Five ounces? Great! I thought we'd only found three." You never know if a defendant's friend or family member might be listening.