“Sniper At Work” road sign, referring to the infamous IRA South Armagh sniper team, notable for their use of .50 caliber Barrett sniper rifles, Northern Ireland; ca. 1990’s
The South Armagh Sniper is the generic name given to the members of the Provisional Irish Republican Army’s (IRA) South Armagh Brigade who conducted a sniping campaign against British security forces from 1990 to 1997. The campaign is notable for the snipers’ use of .50 BMG calibre Barrett M82 and M90 long-range rifles in some of the shootings.
The IRA sniping activities further restricted the freedom of movement of the British Army in South Armagh by hindering their patrols. The MoD issued a new type of body armour, which was both expensive (£4,000) and too heavy (32 lbs) for use on patrol. The morale of the troops was so low that some servicemen had to be disciplined for remaining in shelter while under orders to check vehicles.
A Highway Code-style sign saying “SNIPER AT WORK” was mounted by the IRA near Crossmaglen and became an icon of the republican cause.
(Source)