The cross stitch monogram on the corner of the handkerchief is entirely optional, but it's a very easy way to personalize something. I put an "M" on my handkerchiefs but you could certainly try any letter or number you please.

Cross Stitch 

Below is a brief lesson on how to do very simple cross stitch. I am by no means a cross stitch expert so this may not the official way to do things, but works for me.

On the graph paper below, the odd numbers represent where your needle comes out and the even numbers represent where it goes in:

Here is how to cross stitch if you're making a row that's going up:

Repeat this in the next square above until you have a row of your desired length.

The back should be two neat vertical rows, no crosses.

And here's how to do rows that go down:

The Monogram 

Draw a 1-inch letter at the corner of your handkerchief with a water soluble fabric marker.

Cross stitch the letter using the pen mark as a guide. It's a lot harder to cross stitch on something that doesn't have a grid so take your time placing each stitch. To cross stitch diagonally just follow the instructions for either the up or down row (depending on the direction you're going) but place your #1 point diagonally from your #4 point instead of above or below. Make sure not to pull too tight. 

Once you're done with your monogram carefully weave in the ends in the back. Spray with water and iron to get rid of the blue marker.

All done!