You do need to push.. You will hear a scraping noise which is not scratching the glass, but putting a layer of titanium on the glass.
There is a artist who has an S with a swirl on the tail of the S. Josh Simpson signs his smaller marbles with just an S...
Use a scrap piece of glass or a marble that didn't come out to practice on. The more you do it, the smaller you will be able to write. Just like doing glass.. Practice, Practice,Practice..
I tried to to come up with a signiture that was made up of straight lines to make it easier to write ( MMM ) But then the date changed to 08 and I have to do circles anyway which I find harder...
It will come to you...Good luck..
Joe