There are five features of old advertising signs that determine their value: condition, size, brand, design rarity and demand. The most valuable signs will have a high demand if they are fairly rare or have an aesthetically pleasing appearance.
Condition is the main factor in determining the value of a sign. Signs are given a grade between one and 10 based on their conditions. A sign in excellent condition is graded at a 10, and it could be valued 10 times higher than the same sign that is graded at a six or seven.
The size of a sign is also very important. The most valuable signs are usually between 30 and 42 inches. If a sign is bigger than 42 inches, it will be harder to transport, which decreases the demand.
The brand being advertised can make a big difference in the value. While rare signs are more valuable, they still need to display a well-known brand to be worth more.
Interesting designs and vibrant colors will also increase the value. The most valuable signs will almost always be exceptionally pleasing to the eye.
Rarity is an important factor in determining the worth of a sign. The harder it is to find a particular sign, the more valuable it will be.
All of these aspects either increase or decrease the demand for antique advertising signs. If the demand is high, the value will also be high.