You should never cook directly on a germy public grill.
All it takes to protect your precious patties is to build a fire first. Let it burn for about 10 minutes to incinerate any funky bits left by previous grillers. A charcoal fire reaches about 500 degrees. Most bacteria die at around 165 degrees. Then grab a wad of crumbled up foil with tongs and scrub off the ashes and bring on the burgers!