M8A1 bayonet scabbards. This is the scabbard for the World War II trench knife M3, the carbine bayonet M4, the M1 rifle bayonet M5 and M5 A1, the M 14 bayonet M6, and the M-16 bayonet M7. Any of these bayonets will fit in this scabbard.
I also did not know this one, but I cannot make out the characters that 'I believe' you are asking for in the first picture. As a post 1960 bayonet, I'm assuming it's some DoD RFP code particular to a company doing EMD but that is A TOTAL GUESS.