Color Codes

One nice thing about the end of the world is that you don't have to stop for traffic lights anymore, but the memory of traffic lights have been kept alive in the color codes that people in the Boomlands have developed to talk about fallout zones and the "trail sign" system that Diner Punks use to mark which roads are clear and which ones are dangerous. As a general rule, Red is bad, Green is good, and Yellow is somewhere in between. For some systems, additional colors are added for nuance or to describe additional conditions or cases.

Fallout Zones

Rating the level of fallout in a particular area as red, orange, or yellow probably started based on someone's vague memory of a Cold War map, but adding green as the color of unaffected areas brought ths system in lline with the traffic light code. People talk about yellow zones and red zones and most Diners have a map somewhere with color-coded fallout zones. When someone uses a color to refer to a patch of land, here's what they mean:

Red Zones: Red zones are the areas in and around the craters where the bombs dropped, usually taking the form of a big burned-out hole full of glassy ground, rubble, and things that will kill you. The radiation in red zones is so high that it will kill after a few hours if you're lucky enough to avoid the firestorms, mutants, and other hazards of the zone. Even a few minutes in these areas can lead to radiation sickness, mutation, or slow, lingering death.
Orange Zones: Orange zones are the still-radioactive areas around red zones. The radiation here won't kill you for a few days or weeks, but spending more than a day or two here will shave some time off of your life even if it doesn't leave you with a permanent reminder of your time in the orange zone.
Yellow Zones: Yellow zones are areas where the typical level of radiation is survivable long-term, but which routinely get hit by new fallout transported by weather and water. You can live here as long as you have a secure place to hide and a way to protect your food and water supply when the fallout rolls through.
Green Zones: Green zones are the sections of the Boomland that avoided the worst of the fallout. Radiation levels are only slightly higher than they were before the Boom, most food and water is safe, and most of the animals have the right number of legs in the right places. Appropriately enough, envy is the biggest threat to green zone camps, especially those with easy access to food, water, and trade. Sooner or later, somebody's going to decide they want your land, or at least its bounty.

Road Markers

Road markers started out as a way for convoys to mark routes for their own benefit, but CB chatter and Radiation Radio made it universal. Most road markers consist of a piece of colored cloth tied around a signpost, telephone pole, or tree. Paint--which has the added benefit of allowing a written message--is also sometimes used. In addition to colors, other items are sometimes used to communicate with other travelers. For example, most diner punks who see a deer antler strapped to a road sign will recognize it as a "Deer Crossing" warning. Common colors and symbols include:

Red: Dangerous/Impassible. Find another route. Used to mark roads leading to washouts, radiation, collapsed bridges, bandit routes, etc.
Orange : Dangerous but survivable. Find another route if possible. If you have to keep going, move fast but carefully and keep your eyes open. This basically means the bridge ahead is only about to collapse. If you're lucky, it'll hold up for one more trip across.
Yellow: Proceed with caution. This is used to mark bad roads where you need to move slow to avoid the potholes, debris, and other road hazards.
Green: Smooth sailing ahead. Push down the pedal and enjoy the ride.
Blue: Clean water
Roadkill or Animal Bits: Wildlife crossing.
Gas Pump Nozzle: Fuel available for trade ahead.

Other Uses

Open/Closed: Camps often post flags at their gates to let outsiders know whether it's worth knocking. Green means they're willing to talk to outsiders, yellow means they're open to trade but won't allow strangers inside, and red means keep moving.
Grave Markers: Roadside graves are marked with a black cloth tied to a piece of wood or rebar driven into the ground.
Warning Systems: Camps with a reasonably steady power supply sometimes hang a working traffic light in a prominent location to serve as a warning beacon. Yellow means everyone should check in at headquarters for more information. Red means grab your gun.
Access Warnings: Diners and camps sometimes color code their doors for visitors. Red means "Do Not Enter"; Yellow means "if you're allowed here, you already know it"; Green means open to the public.