Outdoor warning signs are used to signal major obstacles, hazards and dangers requiring the attention of the general public. There are acts like the ""Health and Safety Regulations" which dictate the mandatory display of such signs in the presence of obstacles that can't be removed by any natural process. These signs have to adhere to certain prefixed formats and must include the presence of graphical symbols.

Outdoor road signs for safety and public welfare

Warning signs are generally based on the Vienna Convention on Road signs and Signals (UNECE). The purpose of this committee was to design outdoor signs which have standard and uniform signage which minimises accidents.

Road danger signs, prohibitive signs and mandatory signs are some of the sub groups of warning signage. Road danger signs are employed if there is a condition causing a threat to public health or safety on the roads. Some examples of this type are "frozen bridge", "sharp turn ahead", "slippery when wet" and "40% down grade".

 These sign boards act as lifesaver to truck drivers and users of heavy vehicles driving at high speed. Another variation of road warning signs like "tractor ahead" is used when commercial vehicles like tractors, snow trucks and forklifts are obstructing roads.

Signs such as "fork bends ahead", "unprotected level crossing", "two-way roads" are also used in different situations.

Prohibitive outdoor signs

Prohibitive signs are used in situations that require that individuals/groups don't act in a certain way or refrain from indulging in a particular activity. Common examples are the signs used in parking lots that say "no right", "no left turn", "no parking zone" to guide and protect drivers of vehicles who are using that parking lot.

Outdoor signs are used in construction areas when there are possible areas of danger or potential threats.

There are signs like "WIP (work in progress), don't cross" or "high powered voltage; don't touch" which warn people working in that area to be aware of the restricted areas. Generally, death skull graphics or a prominent Red Cross symbol accompanies prohibitive signs.

Mandatory outdoor signs

Mandatory signs are used with the word "only" at the bottom. These signs are supposed to be displayed compulsorily, failing which the person responsible for that area will have to pay a fine. A good example is "wild fowl passing" signs at the junctions of roads adjoining national parks and wildlife protected areas. These signs warn drivers to drive slow and refrain from hurting animals.

Standard appearance of outdoor warning signs

The appearance of mandatory warning signs has to follow the rules and regulations set by the Vienna convention. Either the sign will be a light blue circle with a pristine white border or the sign will be a white circle with a red border.

The sign boards will be of minimum size of 1.96 feet (across) on semi rural or country side roads. Traffic dense areas should have signs which measure at least 1.31 feet across. Some general warning signs have a prominent exclamatory mark with a brightly coloured background.