Who was 'HD' ?

This is the second bedroom/studio/study window.  It is an old Crittall window and it holds a bit of a mystery; for some reason I haven't really thought about it until now. 

It has some initials etched on one of the panes, the 3rd from the right, 2nd row down to be precise.

The way my mind has worked while staring at these, procrastinating over my studies is as follows:

The initials are etched on the outside of the glass.

They are old fashioned style which dates them.

They are on the opening side of the window, so couldn't have been done easily by leaning out of the window; whoever did them must have been out side.

Below this window is what was originally an added-on lean-to kitchen.

I thought about this, and now I have a vision in my head of a kid climbing up on to the kitchen lean-to roof and sitting by the window, maybe shooting at birds with his catapult, and idly etching his initials on the pane. (I'm assuming it was a boy but I suppose it could have been a tomboy girl). 

I started wondering who he was?

A son of the house? I suppose it must have been his/siblings bedroom window as there are only 2 bedrooms   Maybe it was a trouble-making friend messing around?  

Did he get into trouble?   there wasn't much that could have been done about it other than replace the pane; and given that this was a modest cottage (dating back to early-mid 1800s) originally inhabited by staff from one of the local manor houses, I doubt there was the money for that.

What do you think?