The El Reno and Yukon Walmarts are a popular stop for them. They park far away from anything else and go into the store one at a time. They dress pretty normal except for the combat boots. They also don't like you watching them trying to figure out what they are.
WMD teams. A friend of mine used to be on one. They usually aren't doing anything at all other than road testing their vehicles/cruising and acting operator as F*** so people will wonder who they are and what they are doing. They do clean their crap more than firemen and workout/train all the dang time.