How do I write/paint a message on a glass bird figurine? PAINTERS/ARTISTS ONLY?

Hi everyone,
This is to follow up on a recent questions I asked…To make a long story short, my g/f loves these birds and she collects them..her birthday is coming up soon and we decided not to spend a lot on each other..she was telling me a couple of months ago that she wanted one of these birds and after a lot of votes, I bought this one…….

I would like to write/paint a small message on the glass bird figurine but I’m not sure what type of paint, or brush, or possible ink, or gel pen to use. It is very smooth glass as you can see from the picture. Can anyone tell me what type of paint/pen/brush to use to write a message on it? Since this is very important, I would like ONLY PAINTERS/ARTISTS to help me out. Thank you for your help, I will keep everyone updated