The Second Boot

The second piece of footwear, I found taped to the inside of my bedroom window. On the second storey of the house.

Thankfully, this one contains no operator symbols, and doesn't appear to have been written with a sharpie.

It's a little hard to tell. There's a sort of spirally pattern up at the top. Looks like a shell.

The rest is a quote from Hamlet.
This above all — to thine own self be true;
And it must follow, as the night the day,
Thou canst not then be false to any man.

The image in the bottom right hand corner is a bird of some sort.

Three guesses as to whom the letter is from.