I've mostly noticed it at small outstations, although some hubs have special areas/lines for Silvers--for example, at MSP, FO has a special check in line and then (this isn't publicized) they can go to the opposite end of the airport and use the all-airline elite security line (but not the DL SP security line unless they are eligible for PreCheck, although I don't know how they would prove this to the DL staff member serving as SP line dragon, who does check eligibility for the SP area).