Geez, in our units a marker would never show up on the heavily cammied faces. After a while in the field it was mostly dirt but still.
When I was a scout PSG, we used to get yanked for OPFOR duty all the time, especially for National Guard units. I used to either steal their weapons (especially crew served) and our CO would require their CO to come and pick it up at some later date, with the appropriate amount of ribbing. Often, if I didn't feel like actually taking a vehicle, I'd just use soap to put some derrogatory remark on the windshield.
I've had as much as 10 cases of beer (that I knew of) on my head as a bounty to anyone who could capture me. Nobody ever did but I was tempted to split the bounty and turn myself in sometimes
Most of their line companies were pretty good but once we got by them the REMFs were just what you'd expect. My favorite mission was a snatch mission where they'd give us the name of somebody and our job was to capture him and return him to our BN HQ. Once, when we got a new BN CDR, he gave us a Battalion Commander's name and I delivered him wrapped in a poncho right to my Colonel's position. His jaw dropped when our Lt. and I woke him up to tell him that the misssion was accomplished and there was a package outside for him. I disappeared quickly before they unwrapped the package though. I did hear that there was quite a ruckus though.