You could pack the charset(letters and numbers) in a texture, the same way as flipbook sprite sheets work. Then you could sample this texture, picking the right symbol. You would need to perform that times number of symbols in your text. You would pass a float value,corresponding to ID of letter, for each symbol of your text via dynamic material instance. Obviously it is a no-go for anything longer then a few symbols, but it works pretty good for some sort of random markings and especially if you only need numeric symbols.