<human>: Can you succinctly summarize the text in 1-3 sentences?

Earlier in high school, we went on a field trip to a museum.  The museum was full of WWII/DDay/Vietnam/Korean/etc stuff (like any other museum).  After we took a tour through the museum, we ended up in the gift shop.  One of my friends spotted this army helmet that was relaxing on a table next to some merchandise.  He put it on his head and walked out.  Nobody working in the gift shop saw him.  When we got back on the bus, our teacher asked him where he got it.  He simply said he bought it from the gift shop, but there wasn't a tag on it or price sticker.  He later sold the army helmet for $5 to another friend of mine (who still has it).  We've always wondered whether or not this helmet was real.  

So Reddit, can any of you historians/history lovers share some information about this helmet?  Is it an American made helmet?  What do the symbols/numbers inside it mean?

[The helmet](
<bot>: Went on field trip in high school. Friend stole a helmet from a museum gift shop. Is it a real helmet or a cheap/fake reproduction? Thoughts/comments.