Not seen this before.It's on what is represented as a 1985 Softail.
Do you know what it's origin might be?

 

That is an engine number which is similar to the VIN number.
I believe that engine is from an 85 softail.

http://www.harley-performance.com/harley-vin.html

 

Got it.
I think.
thanks for the link. That is a great reference.

 

here's a screen cap from the owner's manual:





the abbreviated vin should match the full vin, as long as it's the original engine and frame. the manual here doesn't go into it as much, but the 1HD1 means that it was made here in america for the american market and is a 'heavyweight' bike. so your's appears to be a 1985 softail standard.