abstract
army
background
barb
barbed
barbwire
barrier
black
border
boundary
cage
chain
circle
construction
crime
danger
design
element
fence
forbidden
freedom
graphic
guard
illustration
iron
isolated
isolation
jail
line
metal
military
pattern
prison
protection
safety
seamless
secure
security
shape
sharp
silhouette
steel
symbol
texture
war
warning
white
wire
wired