alarm
alert
art
background
black
blue
brake
bubble
caution
contour
control
danger
device
emergency
equipment
fire
handle
help
icon
illustration
isolated
lever
line
linear
lineart
metal
metro
object
outline
protection
pull
railway
red
rescue
safe
safety
security
sign
speech
stop
switch
system
technology
train
transport
transportation
vehicle
wall
warning