I'm probably wrong as heck, & I am sure someone will cuss me out for saying this.
But I use a fine ball point pen with black ink, when I trace my pattern to be cut from a side of leather.
Time you cut your project out & then bevel/edge the sides, you cut the ink trace lines off when round you edges with a edger.
Also I use multiple ways of marking, depending on the job I am getting ready to perform.