Usually they say "warning" on them, in bright red and white.
Warning sign. pretty much all traffic signs with a yellow background are warning or an orange back ground. but there are a couple warning signs that have a white background
Normally green and white
there are no warning signs
Green signs are not warning signs. They are signs that tell you it is "safe" to do something.
Stop signs and Warning/Guiding signs. You must make a complete stop at a stop sign BEFORE the solid white line.
US standard traffic warning signs are yellow background with black symbols or letters. Traffic warning signs in other countries are generally white or yellow background with a red or black border in a triangular shape. Industrial warning signs are various colors, including OSHA and ANZI standards with orange background and black lettering. A yellow OSHA or ANZI sign would mean "caution" not "warning".
It depends on what warning signs that you are interested in. Many sites offer guides on how to spot the warning signs for illnesses etc. If it is to do with motoring check the highway site for details.
Early warning signs of storms and precautions
There are many warning signs of pregnancy. Some warning signs include tingling nipples, spotting, cramping, morning sickness, swollen breasts, a missed period, and/or darkened nipples.
Warning signs are usually a sign that something will be or has the possibility of occurring. They are also called symptoms when dealing with sickness.
There are many warning signs that you are experiencing a lack of oxygen. Some warning signs can include skin that is bluish to gray in color, lightheaded feeling, and tingling in extremities such as fingers or toes.