accident

alarm

alert

ambulance

arrest

blue

car

city

cleanup

collection

crime

danger

dump

ecology

emergency

environment

environmental

equipment

flash

flasher

flashing

garbage

help

industrial

industry

law

light

machine

night

patrol

plastic

police

pollution

recycle

recycling

red

rescue

road

rubbish

safety

security

service

signal

siren

street

traffic

transport

transportation

trash

truck

urgency

vehicle

warning

waste

work