Warn following drivers by flashing your brake lights. Don't stop suddenly. Drivers often do not realize how fast they are catching up to a slow vehicle until they are very close. If you must drive slowly, alert following drivers by turning on your emergency flashers if it is legal. Don't Direct Traffic.
Some drivers try to help out others by signaling when it is safe to pass.
You should not do this. You could cause an accident. You could be blamed and it could cost you many thousands of dollars. Other drivers may not notice your vehicle even when it's in plain sight. Let them know you're there to help prevent accidents.