alert
approach
area
attention
barricade
barrier
beware
block
border
boundary
caution
civil engineering
closed
construction
danger
direction
ditch
dusty
forbidden
ground
heed
hole
industrial
industry
keep out
manufacturing
obstacle
outdoor
prohibition
protection
red
safety
secured
security
sign
signal
soil
stop
stripes
structure
symbol
terrain
traffic
trench
triangle
warn
work in progress
workplace
works
zone