U.S. World War II-era Civil Defense helmet, specifically designated aux police

Of course. This is a fantastic piece of American home front history. Here is my analysis based on your photos.

Identification

This is a U.S. World War II-era Civil Defense helmet, specifically designated for a member of the Auxiliary Police.

Here are the features that identify it:

• The Decal: The circular decal is the most important feature. The logo of a white triangle in a blue circle was the national emblem of the U.S. Office of Civil Defense (OCD) during WWII. The specific symbol inside the triangle indicated the wearer's role. The red shield on your helmet was the official insignia for the Auxiliary Police.
• The Helmet Shell: The helmet itself is a U.S. M1917A1 "Brodie" style helmet. These were the standard issue helmets for the U.S. military during World War I and the beginning of WWII. As the new M1 helmet became standard for the army, vast quantities of these older M1917A1s were repainted (usually white, but sometimes other colors) and repurposed for Civil Defense use on the home front.
• The Liner: The simple liner made of a fiber-like material and fabric suspension is typical for these Civil Defense helmets. They were produced more cheaply than military-grade liners and are often found in a deteriorated state.

Estimated Age

This helmet dates specifically to the World War II period, circa 1941-1945. The Office of Civil Defense was established by President Franklin D. Roosevelt in May 1941 to coordinate the protection of American civilians and infrastructure in the event of an enemy attack. These helmets were a direct result of that effort.