Unfortunately, cashiers, bank tellers etc.. Write the amount on bills when they're counting. I did it as a bartender way back when. We didn't know any better.
@vbmg152, I think cashiers, and bank tellers etc. the reason why they may write on a bill note. They may not want to lose track of how much they counting out, or maybe how much they may need to put in they register or drawer. I think this maybe their way as a little reminder to them, that they counted out the right amount.