Are you sure it was converted? It has an M1 blade it looks like. The M5/M5A1 blade is the same as a M1 Carbine bayonet blade. If it's a M1905/M1942 blade you're thinking of it still looks like a genuine M1 bayonet. The bayonets converted from the longer bayonets have the fuller groove all the way to the tip. Yours is not like that.
If its on the guard (left or right side) it's probably Greek from the CMp haul. Greek bayonets sometimes had a Greek letter and then serial # to the rifle they were paired with. Hand stamped and can be found with a number or letter sometimes ground off then reapplied. The reason is that M1 bayonets were known for poor fit and the Greeks kept them with a particular rifle.
Cutdown bayonets were 1905E1's and they had them too.
Thanks for the response. It was what I wanted to find out about, the E 4400, marking. Also, in looking at the groove it seems that this is a later made M1, not a cut down M5. I appreciate the enlightenment. Thanks again.
This seems to be the best thread for my question. I obtained a curiosity bayonet from SARCO which looks like a standard M5, except for the aluminum grips. It was advertised as a Turkish modification. It has no manufacturer’s mark, or the US M5 stamp. The only mark is EC074. Any additional information would be appreciated.