That is not a simple task for any generative program. Text of any kind is rough, did you try it in other generative programs? What was the result?
The only way possible at this time in Firefly is to create a structure reference with the lettering on a sign. Generative programs can't even get hands right, let alone understand text at this point.
Though it seems that generating text should be a simple task for a Gen AI program, apparently it's not. The results are usually garbled gibberish. For now, you'll have to create the text in another program.