I saw another post like this and members were talking about dog nail polish on the top of the chicks heads. To me that is just asking for chicks to peck each other because they don't like anything that looks different.
I'm waiting until they are older and will be putting clips around their legs if I still can't tell them apart. I had planned on naming them by now but honestly I think it's kind of a good thing. My daughter hasn't gotten attached yet so if something happens it won't be such a heartbreaking ordeal.
I too was going to say the best way to "mark" a chicken is to leg band it but when they are just tiny chicks, dont think that this would be possible as the bands are too big.
I also agree that if you put something very distinctly different, it could encourage the other chicks to peck at it.
First few days I painted their nails different colors. Had to repaint each day but no major pecking at their toes, even the pullet with red polish. Once older I took mini zip ties, painted those with same colors that their toes were and made sure it was loose enough that they could wear em about 1-2 weeks before i snip them off and replace them. Works wonderfully for me and my 12 buffs and sex links.