My kids all did lots of craft and paint and fine motor skill stuff like lego, but non of them could really draw letters until around 4.
ds had a fist grip and scribbled at 3.9, and then suddenly at 4 he changed his grip and started to draw and write his name, all in about 2 months
dd1 was slightly better, I think she was 3/3,5
dd2 was unable to form the letters until at pre-school, her 4th birthday was nov, and in her thank you cards she wrote her initial. By christmas she wrote her whole name.
All of them are now at school, and they were well ahead in their peer group in reception.
I think dd2s friend could write her name around 3.
It is so unimportant if they are making letters. The skill they need is fine motor skill, that comes from playing with lego, playdough, crayons, picking up raisins, using pegs etc etc. Then when you do introduce their name, they will be able to do it.