use a hot wire foam cutter, make one it is fun
thanks! i think that i can work with that.
If the font or letters size proposed on lettersforconcrete.com don't meet your need, you could use a 3D printing service for custom letters or logo. With a positive print in ABS you could cast polyurethane negatives to put in your mold.
Tape and a exacto knife !!! Or Places like Michaels art stores sell them.
I don't know where you live but I use a waterjet cutting service for this kind of stuff. they can cut anything with precision