In the 1940s, the military began employing luminous markers filled with radium paint. This paint consisted of Ra226 salts (likely sulfate or bromide), copper activated zinc sulfide phosphor, and a binding agent like nitrocellulose. 

These markers would either be clipped or tied onto the front or back of paratrooper's helmets, and sometimes sewn onto tunics. They would come in a lead lined box of 24.

Each marker has a radium activity of around 10-20 microcuries. These are not harmful to handle short term, but it's not something you want to wear around for days on end.

Within 5 years of manufacturing these markers, high energy alpha particles from radium and its decay progenies damage the crystalline structure of the phosphor, causing the crystals to shatter into smaller pieces. That is the biggest reason why these do not glow anywhere near as well as they used to when first made. However, if you let your eyes fully adjust to the dark for ~20 minutes, you can easily see them glowing.

These two markers are the best condition ones I have in my collection. I have around 5 of these Type 1 markers.

Alongside the Type 1 disks, were the Type 2 and Type 3. Both of the latter types are much larger and don't have holes to tie string through. The Type 2 was manufactured by the Corps of Engineers for marking stream crossing bridges and trucks- they were fitted with a large bolt and nut on the back. The Type 3 was utilized by the Navy to mark decks and personnel at night. It is equipped with a middle prong to wear on personnel, alongside two prongs that extend on each side to be screwed onto deck bulkheads. I am actively searching for a Type 2 and Type 3 for my radioactive collection.


Frontside of disks
 

Backside of disks


Disks phosphorescing under 365nm UV


50.3mR/h (or 503uSv/h) on contact with a gamma scintillator
 

Here are two Type 2 luminous markers bolted onto the back of a Weapons Carrier. They used the reflector bolts to mount them to the back of the truck.

7 hours ago, robinb said:

Here are two Type 2 luminous markers bolted onto the back of a Weapons Carrier. They used the reflector bolts to mount them to the back of the truck.

Thank you!! I do a lot of research into these markers so finding new info and photos like this is extremely useful!

Lead lined steel box for Type 1 discs.

Lead lined steel box for Type 3 discs.

Paper Navy box for Type D1 markers. With instruction paper and individual cloth pouches for the discs.